diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index f8567e95f98be..bf6b5e6a2edc6 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -35,6 +35,7 @@ config ARM
 	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
+	select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF
 	select ARCH_USE_MEMTEST
@@ -74,7 +75,7 @@ config ARM
 	select HAS_IOPORT
 	select HAVE_ARCH_AUDITSYSCALL if AEABI && !OABI_COMPAT
 	select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6
-	select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU
+	select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU && !PREEMPT_RT
 	select HAVE_ARCH_KFENCE if MMU && !XIP_KERNEL
 	select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU
 	select HAVE_ARCH_KASAN if MMU && !XIP_KERNEL
@@ -119,6 +120,7 @@ config ARM
 	select HAVE_PERF_EVENTS
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
+	select HAVE_POSIX_CPU_TIMERS_TASK_WORK if !KVM
 	select MMU_GATHER_RCU_TABLE_FREE if SMP && ARM_LPAE
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RSEQ
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index fef62e4a9edde..622a30243f4a6 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -404,6 +404,9 @@ do_translation_fault(unsigned long addr, unsigned int fsr,
 	if (addr < TASK_SIZE)
 		return do_page_fault(addr, fsr, regs);
 
+	if (interrupts_enabled(regs))
+		local_irq_enable();
+
 	if (user_mode(regs))
 		goto bad_area;
 
@@ -474,6 +477,9 @@ do_translation_fault(unsigned long addr, unsigned int fsr,
 static int
 do_sect_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 {
+	if (interrupts_enabled(regs))
+		local_irq_enable();
+
 	do_bad_area(addr, fsr, regs);
 	return 0;
 }
diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 7e8773a2d99d0..9fde36fcb80c2 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -55,6 +55,34 @@ extern unsigned int VFP_arch_feroceon __alias(VFP_arch);
  */
 union vfp_state *vfp_current_hw_state[NR_CPUS];
 
+/*
+ * Claim ownership of the VFP unit.
+ *
+ * The caller may change VFP registers until vfp_unlock() is called.
+ *
+ * local_bh_disable() is used to disable preemption and to disable VFP
+ * processing in softirq context. On PREEMPT_RT kernels local_bh_disable() is
+ * not sufficient because it only serializes soft interrupt related sections
+ * via a local lock, but stays preemptible. Disabling preemption is the right
+ * choice here as bottom half processing is always in thread context on RT
+ * kernels so it implicitly prevents bottom half processing as well.
+ */
+static void vfp_lock(void)
+{
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		local_bh_disable();
+	else
+		preempt_disable();
+}
+
+static void vfp_unlock(void)
+{
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		local_bh_enable();
+	else
+		preempt_enable();
+}
+
 /*
  * Is 'thread's most up to date state stored in this CPUs hardware?
  * Must be called from non-preemptible context.
@@ -240,7 +268,7 @@ static void vfp_panic(char *reason, u32 inst)
 /*
  * Process bitmask of exception conditions.
  */
-static void vfp_raise_exceptions(u32 exceptions, u32 inst, u32 fpscr, struct pt_regs *regs)
+static int vfp_raise_exceptions(u32 exceptions, u32 inst, u32 fpscr)
 {
 	int si_code = 0;
 
@@ -248,8 +276,7 @@ static void vfp_raise_exceptions(u32 exceptions, u32 inst, u32 fpscr, struct pt_
 
 	if (exceptions == VFP_EXCEPTION_ERROR) {
 		vfp_panic("unhandled bounce", inst);
-		vfp_raise_sigfpe(FPE_FLTINV, regs);
-		return;
+		return FPE_FLTINV;
 	}
 
 	/*
@@ -277,8 +304,7 @@ static void vfp_raise_exceptions(u32 exceptions, u32 inst, u32 fpscr, struct pt_
 	RAISE(FPSCR_OFC, FPSCR_OFE, FPE_FLTOVF);
 	RAISE(FPSCR_IOC, FPSCR_IOE, FPE_FLTINV);
 
-	if (si_code)
-		vfp_raise_sigfpe(si_code, regs);
+	return si_code;
 }
 
 /*
@@ -324,6 +350,8 @@ static u32 vfp_emulate_instruction(u32 inst, u32 fpscr, struct pt_regs *regs)
 static void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
 {
 	u32 fpscr, orig_fpscr, fpsid, exceptions;
+	int si_code2 = 0;
+	int si_code = 0;
 
 	pr_debug("VFP: bounce: trigger %08x fpexc %08x\n", trigger, fpexc);
 
@@ -369,8 +397,8 @@ static void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
 		 * unallocated VFP instruction but with FPSCR.IXE set and not
 		 * on VFP subarch 1.
 		 */
-		 vfp_raise_exceptions(VFP_EXCEPTION_ERROR, trigger, fpscr, regs);
-		return;
+		si_code = vfp_raise_exceptions(VFP_EXCEPTION_ERROR, trigger, fpscr);
+		goto exit;
 	}
 
 	/*
@@ -394,14 +422,14 @@ static void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
 	 */
 	exceptions = vfp_emulate_instruction(trigger, fpscr, regs);
 	if (exceptions)
-		vfp_raise_exceptions(exceptions, trigger, orig_fpscr, regs);
+		si_code2 = vfp_raise_exceptions(exceptions, trigger, orig_fpscr);
 
 	/*
 	 * If there isn't a second FP instruction, exit now. Note that
 	 * the FPEXC.FP2V bit is valid only if FPEXC.EX is 1.
 	 */
 	if ((fpexc & (FPEXC_EX | FPEXC_FP2V)) != (FPEXC_EX | FPEXC_FP2V))
-		return;
+		goto exit;
 
 	/*
 	 * The barrier() here prevents fpinst2 being read
@@ -413,7 +441,13 @@ static void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
  emulate:
 	exceptions = vfp_emulate_instruction(trigger, orig_fpscr, regs);
 	if (exceptions)
-		vfp_raise_exceptions(exceptions, trigger, orig_fpscr, regs);
+		si_code = vfp_raise_exceptions(exceptions, trigger, orig_fpscr);
+exit:
+	vfp_unlock();
+	if (si_code2)
+		vfp_raise_sigfpe(si_code2, regs);
+	if (si_code)
+		vfp_raise_sigfpe(si_code, regs);
 }
 
 static void vfp_enable(void *unused)
@@ -512,11 +546,9 @@ static inline void vfp_pm_init(void) { }
  */
 void vfp_sync_hwstate(struct thread_info *thread)
 {
-	unsigned int cpu = get_cpu();
+	vfp_lock();
 
-	local_bh_disable();
-
-	if (vfp_state_in_hw(cpu, thread)) {
+	if (vfp_state_in_hw(raw_smp_processor_id(), thread)) {
 		u32 fpexc = fmrx(FPEXC);
 
 		/*
@@ -527,8 +559,7 @@ void vfp_sync_hwstate(struct thread_info *thread)
 		fmxr(FPEXC, fpexc);
 	}
 
-	local_bh_enable();
-	put_cpu();
+	vfp_unlock();
 }
 
 /* Ensure that the thread reloads the hardware VFP state on the next use. */
@@ -683,7 +714,7 @@ static int vfp_support_entry(struct pt_regs *regs, u32 trigger)
 	if (!user_mode(regs))
 		return vfp_kmode_exception(regs, trigger);
 
-	local_bh_disable();
+	vfp_lock();
 	fpexc = fmrx(FPEXC);
 
 	/*
@@ -748,6 +779,7 @@ static int vfp_support_entry(struct pt_regs *regs, u32 trigger)
 		 * replay the instruction that trapped.
 		 */
 		fmxr(FPEXC, fpexc);
+		vfp_unlock();
 	} else {
 		/* Check for synchronous or asynchronous exceptions */
 		if (!(fpexc & (FPEXC_EX | FPEXC_DEX))) {
@@ -762,17 +794,17 @@ static int vfp_support_entry(struct pt_regs *regs, u32 trigger)
 			if (!(fpscr & FPSCR_IXE)) {
 				if (!(fpscr & FPSCR_LENGTH_MASK)) {
 					pr_debug("not VFP\n");
-					local_bh_enable();
+					vfp_unlock();
 					return -ENOEXEC;
 				}
 				fpexc |= FPEXC_DEX;
 			}
 		}
 bounce:		regs->ARM_pc += 4;
+		/* VFP_bounce() will invoke vfp_unlock() */
 		VFP_bounce(trigger, fpexc, regs);
 	}
 
-	local_bh_enable();
 	return 0;
 }
 
@@ -819,7 +851,7 @@ void kernel_neon_begin(void)
 	unsigned int cpu;
 	u32 fpexc;
 
-	local_bh_disable();
+	vfp_lock();
 
 	/*
 	 * Kernel mode NEON is only allowed outside of hardirq context with
@@ -850,7 +882,7 @@ void kernel_neon_end(void)
 {
 	/* Disable the NEON/VFP unit. */
 	fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
-	local_bh_enable();
+	vfp_unlock();
 }
 EXPORT_SYMBOL(kernel_neon_end);
 
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7b071a00425d2..c5210e9b11a20 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -97,6 +97,7 @@ config ARM64
 	select ARCH_SUPPORTS_NUMA_BALANCING
 	select ARCH_SUPPORTS_PAGE_TABLE_CHECK
 	select ARCH_SUPPORTS_PER_VMA_LOCK
+	select ARCH_SUPPORTS_RT
 	select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
 	select ARCH_WANT_COMPAT_IPC_PARSE_VERSION if COMPAT
 	select ARCH_WANT_DEFAULT_BPF_JIT
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 6f105ee4f3cf5..fff3a3788167a 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -166,6 +166,7 @@ config PPC
 	select ARCH_STACKWALK
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_SUPPORTS_DEBUG_PAGEALLOC	if PPC_BOOK3S || PPC_8xx || 40x
+	select ARCH_SUPPORTS_RT			if HAVE_POSIX_CPU_TIMERS_TASK_WORK
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF		if PPC64
 	select ARCH_USE_MEMTEST
@@ -269,6 +270,7 @@ config PPC
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RELIABLE_STACKTRACE
+	select HAVE_POSIX_CPU_TIMERS_TASK_WORK	if !KVM
 	select HAVE_RSEQ
 	select HAVE_SETUP_PER_CPU_AREA		if PPC64
 	select HAVE_SOFTIRQ_ON_OWN_STACK
diff --git a/arch/powerpc/include/asm/stackprotector.h b/arch/powerpc/include/asm/stackprotector.h
index 283c346478565..4727f40052ddd 100644
--- a/arch/powerpc/include/asm/stackprotector.h
+++ b/arch/powerpc/include/asm/stackprotector.h
@@ -19,8 +19,13 @@
  */
 static __always_inline void boot_init_stack_canary(void)
 {
-	unsigned long canary = get_random_canary();
+	unsigned long canary;
 
+#ifndef CONFIG_PREEMPT_RT
+	canary = get_random_canary();
+#else
+	canary = ((unsigned long)&canary) & CANARY_MASK;
+#endif
 	current->stack_canary = canary;
 #ifdef CONFIG_PPC64
 	get_paca()->canary = canary;
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 5ea2014aff90d..9cffe23e93572 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -261,12 +261,17 @@ static char *get_mmu_str(void)
 
 static int __die(const char *str, struct pt_regs *regs, long err)
 {
+	const char *pr = "";
+
 	printk("Oops: %s, sig: %ld [#%d]\n", str, err, ++die_counter);
 
+	if (IS_ENABLED(CONFIG_PREEMPTION))
+		pr = IS_ENABLED(CONFIG_PREEMPT_RT) ? " PREEMPT_RT" : " PREEMPT";
+
 	printk("%s PAGE_SIZE=%luK%s%s%s%s%s%s %s\n",
 	       IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN) ? "LE" : "BE",
 	       PAGE_SIZE / 1024, get_mmu_str(),
-	       IS_ENABLED(CONFIG_PREEMPT) ? " PREEMPT" : "",
+	       pr,
 	       IS_ENABLED(CONFIG_SMP) ? " SMP" : "",
 	       IS_ENABLED(CONFIG_SMP) ? (" NR_CPUS=" __stringify(NR_CPUS)) : "",
 	       debug_pagealloc_enabled() ? " DEBUG_PAGEALLOC" : "",
diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
index 902611954200d..2f188137f830f 100644
--- a/arch/powerpc/kvm/Kconfig
+++ b/arch/powerpc/kvm/Kconfig
@@ -224,6 +224,7 @@ config KVM_E500MC
 config KVM_MPIC
 	bool "KVM in-kernel MPIC emulation"
 	depends on KVM && PPC_E500
+	depends on !PREEMPT_RT
 	select HAVE_KVM_IRQCHIP
 	select HAVE_KVM_IRQFD
 	select HAVE_KVM_IRQ_ROUTING
diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/pseries/Kconfig
index afc0f6a613372..dc3f63c2687d4 100644
--- a/arch/powerpc/platforms/pseries/Kconfig
+++ b/arch/powerpc/platforms/pseries/Kconfig
@@ -2,6 +2,7 @@
 config PPC_PSERIES
 	depends on PPC64 && PPC_BOOK3S
 	bool "IBM pSeries & new (POWER5-based) iSeries"
+	select GENERIC_ALLOCATOR
 	select HAVE_PCSPKR_PLATFORM
 	select MPIC
 	select OF_DYNAMIC
diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
index 496e16c588aaa..05cee07aafbbb 100644
--- a/arch/powerpc/platforms/pseries/iommu.c
+++ b/arch/powerpc/platforms/pseries/iommu.c
@@ -25,6 +25,7 @@
 #include <linux/of_address.h>
 #include <linux/iommu.h>
 #include <linux/rculist.h>
+#include <linux/local_lock.h>
 #include <asm/io.h>
 #include <asm/prom.h>
 #include <asm/rtas.h>
@@ -206,7 +207,13 @@ static int tce_build_pSeriesLP(unsigned long liobn, long tcenum, long tceshift,
 	return ret;
 }
 
-static DEFINE_PER_CPU(__be64 *, tce_page);
+struct tce_page {
+	__be64 * page;
+	local_lock_t lock;
+};
+static DEFINE_PER_CPU(struct tce_page, tce_page) = {
+	.lock = INIT_LOCAL_LOCK(lock),
+};
 
 static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
 				     long npages, unsigned long uaddr,
@@ -229,9 +236,10 @@ static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
 		                           direction, attrs);
 	}
 
-	local_irq_save(flags);	/* to protect tcep and the page behind it */
+	/* to protect tcep and the page behind it */
+	local_lock_irqsave(&tce_page.lock, flags);
 
-	tcep = __this_cpu_read(tce_page);
+	tcep = __this_cpu_read(tce_page.page);
 
 	/* This is safe to do since interrupts are off when we're called
 	 * from iommu_alloc{,_sg}()
@@ -240,12 +248,12 @@ static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
 		tcep = (__be64 *)__get_free_page(GFP_ATOMIC);
 		/* If allocation fails, fall back to the loop implementation */
 		if (!tcep) {
-			local_irq_restore(flags);
+			local_unlock_irqrestore(&tce_page.lock, flags);
 			return tce_build_pSeriesLP(tbl->it_index, tcenum,
 					tceshift,
 					npages, uaddr, direction, attrs);
 		}
-		__this_cpu_write(tce_page, tcep);
+		__this_cpu_write(tce_page.page, tcep);
 	}
 
 	rpn = __pa(uaddr) >> tceshift;
@@ -275,7 +283,7 @@ static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
 		tcenum += limit;
 	} while (npages > 0 && !rc);
 
-	local_irq_restore(flags);
+	local_unlock_irqrestore(&tce_page.lock, flags);
 
 	if (unlikely(rc == H_NOT_ENOUGH_RESOURCES)) {
 		ret = (int)rc;
@@ -459,16 +467,17 @@ static int tce_setrange_multi_pSeriesLP(unsigned long start_pfn,
 				DMA_BIDIRECTIONAL, 0);
 	}
 
-	local_irq_disable();	/* to protect tcep and the page behind it */
-	tcep = __this_cpu_read(tce_page);
+	/* to protect tcep and the page behind it */
+	local_lock_irq(&tce_page.lock);
+	tcep = __this_cpu_read(tce_page.page);
 
 	if (!tcep) {
 		tcep = (__be64 *)__get_free_page(GFP_ATOMIC);
 		if (!tcep) {
-			local_irq_enable();
+			local_unlock_irq(&tce_page.lock);
 			return -ENOMEM;
 		}
-		__this_cpu_write(tce_page, tcep);
+		__this_cpu_write(tce_page.page, tcep);
 	}
 
 	proto_tce = TCE_PCI_READ | TCE_PCI_WRITE;
@@ -511,7 +520,7 @@ static int tce_setrange_multi_pSeriesLP(unsigned long start_pfn,
 
 	/* error cleanup: caller will clear whole range */
 
-	local_irq_enable();
+	local_unlock_irq(&tce_page.lock);
 	return rc;
 }
 
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 95a2a06acc6a6..1ac4a3e6a5fc2 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -49,6 +49,7 @@ config RISCV
 	select ARCH_SUPPORTS_HUGETLBFS if MMU
 	select ARCH_SUPPORTS_PAGE_TABLE_CHECK if MMU
 	select ARCH_SUPPORTS_PER_VMA_LOCK if MMU
+	select ARCH_SUPPORTS_RT
 	select ARCH_SUPPORTS_SHADOW_CALL_STACK if HAVE_SHADOW_CALL_STACK
 	select ARCH_USE_MEMTEST
 	select ARCH_USE_QUEUED_RWLOCKS
@@ -137,6 +138,7 @@ config RISCV
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_POSIX_CPU_TIMERS_TASK_WORK
 	select HAVE_PREEMPT_DYNAMIC_KEY if !XIP_KERNEL
+	select HAVE_PREEMPT_AUTO
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RETHOOK if !XIP_KERNEL
 	select HAVE_RSEQ
diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h
index 574779900bfb3..fd9ddc27b29ba 100644
--- a/arch/riscv/include/asm/thread_info.h
+++ b/arch/riscv/include/asm/thread_info.h
@@ -95,6 +95,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
  * - pending work-to-be-done flags are in lowest half-word
  * - other flags in upper half-word(s)
  */
+#define TIF_ARCH_RESCHED_LAZY	0	/* Lazy rescheduling */
 #define TIF_NOTIFY_RESUME	1	/* callback before returning to user */
 #define TIF_SIGPENDING		2	/* signal pending */
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
@@ -109,6 +110,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
 #define _TIF_NOTIFY_SIGNAL	(1 << TIF_NOTIFY_SIGNAL)
 #define _TIF_UPROBE		(1 << TIF_UPROBE)
+#define _TIF_ARCH_RESCHED_LAZY	(1 << TIF_ARCH_RESCHED_LAZY)
 
 #define _TIF_WORK_MASK \
 	(_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | _TIF_NEED_RESCHED | \
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 3762f41bb0929..bd4a63dee459d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -27,7 +27,7 @@ config X86_64
 	# Options that are inherently 64-bit kernel only:
 	select ARCH_HAS_GIGANTIC_PAGE
 	select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
-	select ARCH_SUPPORTS_PER_VMA_LOCK
+	select ARCH_SUPPORTS_RT
 	select HAVE_ARCH_SOFT_DIRTY
 	select MODULES_USE_ELF_RELA
 	select NEED_DMA_MAP_STATE
@@ -116,6 +116,7 @@ config X86
 	select ARCH_USES_CFI_TRAPS		if X86_64 && CFI_CLANG
 	select ARCH_SUPPORTS_LTO_CLANG
 	select ARCH_SUPPORTS_LTO_CLANG_THIN
+	select ARCH_SUPPORTS_RT
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF		if X86_CMPXCHG64
 	select ARCH_USE_MEMTEST
@@ -271,6 +272,7 @@ config X86
 	select HAVE_STATIC_CALL
 	select HAVE_STATIC_CALL_INLINE		if HAVE_OBJTOOL
 	select HAVE_PREEMPT_DYNAMIC_CALL
+	select HAVE_PREEMPT_AUTO
 	select HAVE_RSEQ
 	select HAVE_RUST			if X86_64
 	select HAVE_SYSCALL_TRACEPOINTS
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index d63b02940747f..1ff38ebbd5880 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -81,8 +81,9 @@ struct thread_info {
 #define TIF_NOTIFY_RESUME	1	/* callback before returning to user */
 #define TIF_SIGPENDING		2	/* signal pending */
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
-#define TIF_SINGLESTEP		4	/* reenable singlestep on user return*/
-#define TIF_SSBD		5	/* Speculative store bypass disable */
+#define TIF_ARCH_RESCHED_LAZY	4	/* Lazy rescheduling */
+#define TIF_SINGLESTEP		5	/* reenable singlestep on user return*/
+#define TIF_SSBD		6	/* Speculative store bypass disable */
 #define TIF_SPEC_IB		9	/* Indirect branch speculation mitigation */
 #define TIF_SPEC_L1D_FLUSH	10	/* Flush L1D on mm switches (processes) */
 #define TIF_USER_RETURN_NOTIFY	11	/* notify kernel of userspace return */
@@ -104,6 +105,7 @@ struct thread_info {
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
+#define _TIF_ARCH_RESCHED_LAZY	(1 << TIF_ARCH_RESCHED_LAZY)
 #define _TIF_SINGLESTEP		(1 << TIF_SINGLESTEP)
 #define _TIF_SSBD		(1 << TIF_SSBD)
 #define _TIF_SPEC_IB		(1 << TIF_SPEC_IB)
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 3a34a8c425fe4..1a69f082833ef 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -108,7 +108,7 @@ static const struct dmi_system_id processor_power_dmi_table[] = {
  */
 static void __cpuidle acpi_safe_halt(void)
 {
-	if (!tif_need_resched()) {
+	if (!need_resched()) {
 		raw_safe_halt();
 		raw_local_irq_disable();
 	}
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index d77d3664ca080..d083a5dfb244a 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -57,6 +57,41 @@ static void zram_free_page(struct zram *zram, size_t index);
 static int zram_read_page(struct zram *zram, struct page *page, u32 index,
 			  struct bio *parent);
 
+#ifdef CONFIG_PREEMPT_RT
+static void zram_meta_init_table_locks(struct zram *zram, size_t num_pages)
+{
+	size_t index;
+
+	for (index = 0; index < num_pages; index++)
+		spin_lock_init(&zram->table[index].lock);
+}
+
+static int zram_slot_trylock(struct zram *zram, u32 index)
+{
+	int ret;
+
+	ret = spin_trylock(&zram->table[index].lock);
+	if (ret)
+		__set_bit(ZRAM_LOCK, &zram->table[index].flags);
+	return ret;
+}
+
+static void zram_slot_lock(struct zram *zram, u32 index)
+{
+	spin_lock(&zram->table[index].lock);
+	__set_bit(ZRAM_LOCK, &zram->table[index].flags);
+}
+
+static void zram_slot_unlock(struct zram *zram, u32 index)
+{
+	__clear_bit(ZRAM_LOCK, &zram->table[index].flags);
+	spin_unlock(&zram->table[index].lock);
+}
+
+#else
+
+static void zram_meta_init_table_locks(struct zram *zram, size_t num_pages) { }
+
 static int zram_slot_trylock(struct zram *zram, u32 index)
 {
 	return bit_spin_trylock(ZRAM_LOCK, &zram->table[index].flags);
@@ -71,6 +106,7 @@ static void zram_slot_unlock(struct zram *zram, u32 index)
 {
 	bit_spin_unlock(ZRAM_LOCK, &zram->table[index].flags);
 }
+#endif
 
 static inline bool init_done(struct zram *zram)
 {
@@ -1242,6 +1278,7 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize)
 
 	if (!huge_class_size)
 		huge_class_size = zs_huge_class_size(zram->mem_pool);
+	zram_meta_init_table_locks(zram, num_pages);
 	return true;
 }
 
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index d090753f97bec..833abc17d4140 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -69,6 +69,9 @@ struct zram_table_entry {
 		unsigned long element;
 	};
 	unsigned long flags;
+#ifdef CONFIG_PREEMPT_RT
+	spinlock_t lock;
+#endif
 #ifdef CONFIG_ZRAM_MEMORY_TRACKING
 	ktime_t ac_time;
 #endif
diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
index ce397a8797f7b..98c3f532822d0 100644
--- a/drivers/gpu/drm/i915/Kconfig
+++ b/drivers/gpu/drm/i915/Kconfig
@@ -3,7 +3,6 @@ config DRM_I915
 	tristate "Intel 8xx/9xx/G3x/G4x/HD Graphics"
 	depends on DRM
 	depends on X86 && PCI
-	depends on !PREEMPT_RT
 	select INTEL_GTT if X86
 	select INTERVAL_TREE
 	# we need shmfs for the swappable backing store, and in particular
diff --git a/drivers/gpu/drm/i915/display/intel_crtc.c b/drivers/gpu/drm/i915/display/intel_crtc.c
index 1fd068e6e26ca..8a82a7ebaf1e0 100644
--- a/drivers/gpu/drm/i915/display/intel_crtc.c
+++ b/drivers/gpu/drm/i915/display/intel_crtc.c
@@ -573,7 +573,8 @@ void intel_pipe_update_start(struct intel_atomic_state *state,
 	 */
 	intel_psr_wait_for_idle_locked(new_crtc_state);
 
-	local_irq_disable();
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		local_irq_disable();
 
 	crtc->debug.min_vbl = min;
 	crtc->debug.max_vbl = max;
@@ -598,11 +599,13 @@ void intel_pipe_update_start(struct intel_atomic_state *state,
 			break;
 		}
 
-		local_irq_enable();
+		if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+			local_irq_enable();
 
 		timeout = schedule_timeout(timeout);
 
-		local_irq_disable();
+		if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+			local_irq_disable();
 	}
 
 	finish_wait(wq, &wait);
@@ -635,7 +638,8 @@ void intel_pipe_update_start(struct intel_atomic_state *state,
 	return;
 
 irq_disable:
-	local_irq_disable();
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		local_irq_disable();
 }
 
 #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_VBLANK_EVADE)
@@ -737,7 +741,8 @@ void intel_pipe_update_end(struct intel_atomic_state *state,
 	 */
 	intel_vrr_send_push(new_crtc_state);
 
-	local_irq_enable();
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		local_irq_enable();
 
 	if (intel_vgpu_active(dev_priv))
 		goto out;
diff --git a/drivers/gpu/drm/i915/display/intel_vblank.c b/drivers/gpu/drm/i915/display/intel_vblank.c
index 2cec2abf97466..2e4f0ed417b5a 100644
--- a/drivers/gpu/drm/i915/display/intel_vblank.c
+++ b/drivers/gpu/drm/i915/display/intel_vblank.c
@@ -308,7 +308,8 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc,
 	 */
 	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
 
-	/* preempt_disable_rt() should go right here in PREEMPT_RT patchset. */
+	if (IS_ENABLED(CONFIG_PREEMPT_RT))
+		preempt_disable();
 
 	/* Get optional system timestamp before query. */
 	if (stime)
@@ -372,7 +373,8 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc,
 	if (etime)
 		*etime = ktime_get();
 
-	/* preempt_enable_rt() should go right here in PREEMPT_RT patchset. */
+	if (IS_ENABLED(CONFIG_PREEMPT_RT))
+		preempt_enable();
 
 	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
 
diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
index ecc990ec1b952..8d04b10681f0d 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -312,10 +312,9 @@ void __intel_breadcrumbs_park(struct intel_breadcrumbs *b)
 	/* Kick the work once more to drain the signalers, and disarm the irq */
 	irq_work_sync(&b->irq_work);
 	while (READ_ONCE(b->irq_armed) && !atomic_read(&b->active)) {
-		local_irq_disable();
-		signal_irq_work(&b->irq_work);
-		local_irq_enable();
+		irq_work_queue(&b->irq_work);
 		cond_resched();
+		irq_work_sync(&b->irq_work);
 	}
 }
 
diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
index e8f42ec6b1b47..3274d71a5ce6a 100644
--- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
+++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
@@ -1303,7 +1303,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 	 * and context switches) submission.
 	 */
 
-	spin_lock(&sched_engine->lock);
+	spin_lock_irq(&sched_engine->lock);
 
 	/*
 	 * If the queue is higher priority than the last
@@ -1403,7 +1403,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 				 * Even if ELSP[1] is occupied and not worthy
 				 * of timeslices, our queue might be.
 				 */
-				spin_unlock(&sched_engine->lock);
+				spin_unlock_irq(&sched_engine->lock);
 				return;
 			}
 		}
@@ -1429,7 +1429,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 
 		if (last && !can_merge_rq(last, rq)) {
 			spin_unlock(&ve->base.sched_engine->lock);
-			spin_unlock(&engine->sched_engine->lock);
+			spin_unlock_irq(&engine->sched_engine->lock);
 			return; /* leave this for another sibling */
 		}
 
@@ -1591,7 +1591,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 	 */
 	sched_engine->queue_priority_hint = queue_prio(sched_engine);
 	i915_sched_engine_reset_on_empty(sched_engine);
-	spin_unlock(&sched_engine->lock);
+	spin_unlock_irq(&sched_engine->lock);
 
 	/*
 	 * We can skip poking the HW if we ended up with exactly the same set
@@ -1617,13 +1617,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 	}
 }
 
-static void execlists_dequeue_irq(struct intel_engine_cs *engine)
-{
-	local_irq_disable(); /* Suspend interrupts across request submission */
-	execlists_dequeue(engine);
-	local_irq_enable(); /* flush irq_work (e.g. breadcrumb enabling) */
-}
-
 static void clear_ports(struct i915_request **ports, int count)
 {
 	memset_p((void **)ports, NULL, count);
@@ -2478,7 +2471,7 @@ static void execlists_submission_tasklet(struct tasklet_struct *t)
 	}
 
 	if (!engine->execlists.pending[0]) {
-		execlists_dequeue_irq(engine);
+		execlists_dequeue(engine);
 		start_timeslice(engine);
 	}
 
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
index 2b6dfe62c8f2a..28243efcaec2e 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
@@ -349,7 +349,7 @@ static inline int intel_guc_send_busy_loop(struct intel_guc *guc,
 {
 	int err;
 	unsigned int sleep_period_ms = 1;
-	bool not_atomic = !in_atomic() && !irqs_disabled();
+	bool not_atomic = !in_atomic() && !irqs_disabled() && !rcu_preempt_depth();
 
 	/*
 	 * FIXME: Have caller pass in if we are in an atomic context to avoid
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index f59081066a197..014d02029a415 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -609,7 +609,6 @@ bool __i915_request_submit(struct i915_request *request)
 
 	RQ_TRACE(request, "\n");
 
-	GEM_BUG_ON(!irqs_disabled());
 	lockdep_assert_held(&engine->sched_engine->lock);
 
 	/*
@@ -718,7 +717,6 @@ void __i915_request_unsubmit(struct i915_request *request)
 	 */
 	RQ_TRACE(request, "\n");
 
-	GEM_BUG_ON(!irqs_disabled());
 	lockdep_assert_held(&engine->sched_engine->lock);
 
 	/*
diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h
index ce1cbee1b39dd..3c51620d011b1 100644
--- a/drivers/gpu/drm/i915/i915_trace.h
+++ b/drivers/gpu/drm/i915/i915_trace.h
@@ -6,6 +6,10 @@
 #if !defined(_I915_TRACE_H_) || defined(TRACE_HEADER_MULTI_READ)
 #define _I915_TRACE_H_
 
+#ifdef CONFIG_PREEMPT_RT
+#define NOTRACE
+#endif
+
 #include <linux/stringify.h>
 #include <linux/types.h>
 #include <linux/tracepoint.h>
@@ -322,7 +326,7 @@ DEFINE_EVENT(i915_request, i915_request_add,
 	     TP_ARGS(rq)
 );
 
-#if defined(CONFIG_DRM_I915_LOW_LEVEL_TRACEPOINTS)
+#if defined(CONFIG_DRM_I915_LOW_LEVEL_TRACEPOINTS) && !defined(NOTRACE)
 DEFINE_EVENT(i915_request, i915_request_guc_submit,
 	     TP_PROTO(struct i915_request *rq),
 	     TP_ARGS(rq)
diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
index c61066498bf2f..48e19e55d6b07 100644
--- a/drivers/gpu/drm/i915/i915_utils.h
+++ b/drivers/gpu/drm/i915/i915_utils.h
@@ -288,7 +288,7 @@ wait_remaining_ms_from_jiffies(unsigned long timestamp_jiffies, int to_wait_ms)
 #define wait_for(COND, MS)		_wait_for((COND), (MS) * 1000, 10, 1000)
 
 /* If CONFIG_PREEMPT_COUNT is disabled, in_atomic() always reports false. */
-#if defined(CONFIG_DRM_I915_DEBUG) && defined(CONFIG_PREEMPT_COUNT)
+#if defined(CONFIG_DRM_I915_DEBUG) && defined(CONFIG_PREEMPT_COUNT) && !defined(CONFIG_PREEMPT_RT)
 # define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) WARN_ON_ONCE((ATOMIC) && !in_atomic())
 #else
 # define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) do { } while (0)
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 9127331518587..ba6de401c458e 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -592,6 +592,7 @@ serial8250_register_ports(struct uart_driver *drv, struct device *dev)
 
 #ifdef CONFIG_SERIAL_8250_CONSOLE
 
+#ifdef CONFIG_SERIAL_8250_LEGACY_CONSOLE
 static void univ8250_console_write(struct console *co, const char *s,
 				   unsigned int count)
 {
@@ -599,6 +600,28 @@ static void univ8250_console_write(struct console *co, const char *s,
 
 	serial8250_console_write(up, s, count);
 }
+#else
+static bool univ8250_console_write_atomic(struct console *co,
+					  struct nbcon_write_context *wctxt)
+{
+	struct uart_8250_port *up = &serial8250_ports[co->index];
+
+	return serial8250_console_write_atomic(up, wctxt);
+}
+
+static bool univ8250_console_write_thread(struct console *co,
+					  struct nbcon_write_context *wctxt)
+{
+	struct uart_8250_port *up = &serial8250_ports[co->index];
+
+	return serial8250_console_write_thread(up, wctxt);
+}
+
+static struct uart_port *univ8250_console_uart_port(struct console *con)
+{
+	return &serial8250_ports[con->index].port;
+}
+#endif /* CONFIG_SERIAL_8250_LEGACY_CONSOLE */
 
 static int univ8250_console_setup(struct console *co, char *options)
 {
@@ -698,12 +721,19 @@ static int univ8250_console_match(struct console *co, char *name, int idx,
 
 static struct console univ8250_console = {
 	.name		= "ttyS",
+#ifdef CONFIG_SERIAL_8250_LEGACY_CONSOLE
 	.write		= univ8250_console_write,
+	.flags		= CON_PRINTBUFFER | CON_ANYTIME,
+#else
+	.write_atomic	= univ8250_console_write_atomic,
+	.write_thread	= univ8250_console_write_thread,
+	.flags		= CON_PRINTBUFFER | CON_ANYTIME | CON_NBCON,
+	.uart_port	= univ8250_console_uart_port,
+#endif
 	.device		= uart_console_device,
 	.setup		= univ8250_console_setup,
 	.exit		= univ8250_console_exit,
 	.match		= univ8250_console_match,
-	.flags		= CON_PRINTBUFFER | CON_ANYTIME,
 	.index		= -1,
 	.data		= &serial8250_reg,
 };
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 8ca061d3bbb92..c8d15f659de98 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -550,6 +550,11 @@ static int serial8250_em485_init(struct uart_8250_port *p)
 	if (!p->em485)
 		return -ENOMEM;
 
+#ifndef CONFIG_SERIAL_8250_LEGACY_CONSOLE
+	if (uart_console(&p->port))
+		dev_warn(p->port.dev, "no atomic printing for rs485 consoles\n");
+#endif
+
 	hrtimer_init(&p->em485->stop_tx_timer, CLOCK_MONOTONIC,
 		     HRTIMER_MODE_REL);
 	hrtimer_init(&p->em485->start_tx_timer, CLOCK_MONOTONIC,
@@ -702,7 +707,11 @@ static void serial8250_set_sleep(struct uart_8250_port *p, int sleep)
 	serial8250_rpm_put(p);
 }
 
-static void serial8250_clear_IER(struct uart_8250_port *up)
+/*
+ * Only to be used by write_atomic() and the legacy write(), which do not
+ * require port lock.
+ */
+static void __serial8250_clear_IER(struct uart_8250_port *up)
 {
 	if (up->capabilities & UART_CAP_UUE)
 		serial_out(up, UART_IER, UART_IER_UUE);
@@ -710,6 +719,14 @@ static void serial8250_clear_IER(struct uart_8250_port *up)
 		serial_out(up, UART_IER, 0);
 }
 
+static inline void serial8250_clear_IER(struct uart_8250_port *up)
+{
+	/* Port locked to synchronize UART_IER access against the console. */
+	lockdep_assert_held_once(&up->port.lock);
+
+	__serial8250_clear_IER(up);
+}
+
 #ifdef CONFIG_SERIAL_8250_RSA
 /*
  * Attempts to turn on the RSA FIFO.  Returns zero on failure.
@@ -3320,6 +3337,11 @@ static void serial8250_console_putchar(struct uart_port *port, unsigned char ch)
 
 	wait_for_xmitr(up, UART_LSR_THRE);
 	serial_port_out(port, UART_TX, ch);
+
+	if (ch == '\n')
+		up->console_newline_needed = false;
+	else
+		up->console_newline_needed = true;
 }
 
 /*
@@ -3348,6 +3370,7 @@ static void serial8250_console_restore(struct uart_8250_port *up)
 	serial8250_out_MCR(up, up->mcr | UART_MCR_DTR | UART_MCR_RTS);
 }
 
+#ifdef CONFIG_SERIAL_8250_LEGACY_CONSOLE
 /*
  * Print a string to the serial port using the device FIFO
  *
@@ -3406,7 +3429,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
 	 *	First save the IER then disable the interrupts
 	 */
 	ier = serial_port_in(port, UART_IER);
-	serial8250_clear_IER(up);
+	__serial8250_clear_IER(up);
 
 	/* check scratch reg to see if port powered off during system sleep */
 	if (up->canary && (up->canary != serial_port_in(port, UART_SCR))) {
@@ -3472,6 +3495,143 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
 	if (locked)
 		uart_port_unlock_irqrestore(port, flags);
 }
+#else
+bool serial8250_console_write_thread(struct uart_8250_port *up,
+				     struct nbcon_write_context *wctxt)
+{
+	struct uart_8250_em485 *em485 = up->em485;
+	struct uart_port *port = &up->port;
+	bool done = false;
+	unsigned int ier;
+
+	touch_nmi_watchdog();
+
+	if (!nbcon_enter_unsafe(wctxt))
+		return false;
+
+	/*
+	 *	First save the IER then disable the interrupts
+	 */
+	ier = serial_port_in(port, UART_IER);
+	serial8250_clear_IER(up);
+
+	/* check scratch reg to see if port powered off during system sleep */
+	if (up->canary && (up->canary != serial_port_in(port, UART_SCR))) {
+		serial8250_console_restore(up);
+		up->canary = 0;
+	}
+
+	if (em485) {
+		if (em485->tx_stopped)
+			up->rs485_start_tx(up);
+		mdelay(port->rs485.delay_rts_before_send);
+	}
+
+	if (nbcon_exit_unsafe(wctxt)) {
+		int len = READ_ONCE(wctxt->len);
+		int i;
+
+		/*
+		 * Write out the message. Toggle unsafe for each byte in order
+		 * to give another (higher priority) context the opportunity
+		 * for a friendly takeover. If such a takeover occurs, this
+		 * context must reacquire ownership in order to perform final
+		 * actions (such as re-enabling the interrupts).
+		 *
+		 * IMPORTANT: wctxt->outbuf and wctxt->len are no longer valid
+		 *	      after a reacquire so writing the message must be
+		 *	      aborted.
+		 */
+		for (i = 0; i < len; i++) {
+			if (!nbcon_enter_unsafe(wctxt)) {
+				nbcon_reacquire(wctxt);
+				break;
+			}
+
+			uart_console_write(port, wctxt->outbuf + i, 1, serial8250_console_putchar);
+
+			if (!nbcon_exit_unsafe(wctxt)) {
+				nbcon_reacquire(wctxt);
+				break;
+			}
+		}
+		done = (i == len);
+	} else {
+		nbcon_reacquire(wctxt);
+	}
+
+	while (!nbcon_enter_unsafe(wctxt))
+		nbcon_reacquire(wctxt);
+
+	/*
+	 *	Finally, wait for transmitter to become empty
+	 *	and restore the IER
+	 */
+	wait_for_xmitr(up, UART_LSR_BOTH_EMPTY);
+
+	if (em485) {
+		mdelay(port->rs485.delay_rts_after_send);
+		if (em485->tx_stopped)
+			up->rs485_stop_tx(up);
+	}
+
+	serial_port_out(port, UART_IER, ier);
+
+	/*
+	 *	The receive handling will happen properly because the
+	 *	receive ready bit will still be set; it is not cleared
+	 *	on read.  However, modem control will not, we must
+	 *	call it if we have saved something in the saved flags
+	 *	while processing with interrupts off.
+	 */
+	if (up->msr_saved_flags)
+		serial8250_modem_status(up);
+
+	return (nbcon_exit_unsafe(wctxt) && done);
+}
+
+bool serial8250_console_write_atomic(struct uart_8250_port *up,
+				     struct nbcon_write_context *wctxt)
+{
+	struct uart_port *port = &up->port;
+	unsigned int ier;
+
+	/* Atomic console not supported for rs485 mode. */
+	if (up->em485)
+		return false;
+
+	touch_nmi_watchdog();
+
+	if (!nbcon_enter_unsafe(wctxt))
+		return false;
+
+	/*
+	 *	First save the IER then disable the interrupts
+	 */
+	ier = serial_port_in(port, UART_IER);
+	__serial8250_clear_IER(up);
+
+	/* check scratch reg to see if port powered off during system sleep */
+	if (up->canary && (up->canary != serial_port_in(port, UART_SCR))) {
+		serial8250_console_restore(up);
+		up->canary = 0;
+	}
+
+	if (up->console_newline_needed)
+		uart_console_write(port, "\n", 1, serial8250_console_putchar);
+	uart_console_write(port, wctxt->outbuf, wctxt->len, serial8250_console_putchar);
+
+	/*
+	 *	Finally, wait for transmitter to become empty
+	 *	and restore the IER
+	 */
+	wait_for_xmitr(up, UART_LSR_BOTH_EMPTY);
+
+	serial_port_out(port, UART_IER, ier);
+
+	return nbcon_exit_unsafe(wctxt);
+}
+#endif /* CONFIG_SERIAL_8250_LEGACY_CONSOLE */
 
 static unsigned int probe_baud(struct uart_port *port)
 {
@@ -3490,6 +3650,7 @@ static unsigned int probe_baud(struct uart_port *port)
 
 int serial8250_console_setup(struct uart_port *port, char *options, bool probe)
 {
+	struct uart_8250_port *up = up_to_u8250p(port);
 	int baud = 9600;
 	int bits = 8;
 	int parity = 'n';
@@ -3499,6 +3660,8 @@ int serial8250_console_setup(struct uart_port *port, char *options, bool probe)
 	if (!port->iobase && !port->membase)
 		return -ENODEV;
 
+	up->console_newline_needed = false;
+
 	if (options)
 		uart_parse_options(options, &baud, &parity, &bits, &flow);
 	else if (probe)
diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 61cc24cd90e4b..01b4bed9f9c5d 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2332,13 +2332,10 @@ pl011_console_write(struct console *co, const char *s, unsigned int count)
 
 	clk_enable(uap->clk);
 
-	local_irq_save(flags);
-	if (uap->port.sysrq)
-		locked = 0;
-	else if (oops_in_progress)
-		locked = uart_port_trylock(&uap->port);
+	if (uap->port.sysrq || oops_in_progress)
+		locked = uart_port_trylock_irqsave(&uap->port, &flags);
 	else
-		uart_port_lock(&uap->port);
+		uart_port_lock_irqsave(&uap->port, &flags);
 
 	/*
 	 *	First save the CR then disable the interrupts
@@ -2364,8 +2361,7 @@ pl011_console_write(struct console *co, const char *s, unsigned int count)
 		pl011_write(old_cr, uap, REG_CR);
 
 	if (locked)
-		uart_port_unlock(&uap->port);
-	local_irq_restore(flags);
+		uart_port_unlock_irqrestore(&uap->port, flags);
 
 	clk_disable(uap->clk);
 }
diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index ad4c1c5d0a7f0..90369adc33f03 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -1212,13 +1212,10 @@ serial_omap_console_write(struct console *co, const char *s,
 	unsigned int ier;
 	int locked = 1;
 
-	local_irq_save(flags);
-	if (up->port.sysrq)
-		locked = 0;
-	else if (oops_in_progress)
-		locked = uart_port_trylock(&up->port);
+	if (up->port.sysrq || oops_in_progress)
+		locked = uart_port_trylock_irqsave(&up->port, &flags);
 	else
-		uart_port_lock(&up->port);
+		uart_port_lock_irqsave(&up->port, &flags);
 
 	/*
 	 * First save the IER then disable the interrupts
@@ -1245,8 +1242,7 @@ serial_omap_console_write(struct console *co, const char *s,
 		check_modem_status(up);
 
 	if (locked)
-		uart_port_unlock(&up->port);
-	local_irq_restore(flags);
+		uart_port_unlock_irqrestore(&up->port, flags);
 }
 
 static int __init
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 06414e43e0b53..d6aebf5ebfa21 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -3544,8 +3544,15 @@ static ssize_t show_cons_active(struct device *dev,
 	for_each_console(c) {
 		if (!c->device)
 			continue;
-		if (!c->write)
-			continue;
+		if (c->flags & CON_NBCON) {
+			if (!c->write_atomic &&
+			    !(c->write_thread && c->kthread)) {
+				continue;
+			}
+		} else {
+			if (!c->write)
+				continue;
+		}
 		if ((c->flags & CON_ENABLED) == 0)
 			continue;
 		cs[i++] = c;
diff --git a/fs/proc/consoles.c b/fs/proc/consoles.c
index e0758fe7936dc..2703676549f5e 100644
--- a/fs/proc/consoles.c
+++ b/fs/proc/consoles.c
@@ -21,12 +21,14 @@ static int show_console_dev(struct seq_file *m, void *v)
 		{ CON_ENABLED,		'E' },
 		{ CON_CONSDEV,		'C' },
 		{ CON_BOOT,		'B' },
+		{ CON_NBCON,		'N' },
 		{ CON_PRINTBUFFER,	'p' },
 		{ CON_BRL,		'b' },
 		{ CON_ANYTIME,		'a' },
 	};
 	char flags[ARRAY_SIZE(con_flags) + 1];
 	struct console *con = v;
+	char con_write = '-';
 	unsigned int a;
 	dev_t dev = 0;
 
@@ -57,9 +59,15 @@ static int show_console_dev(struct seq_file *m, void *v)
 	seq_setwidth(m, 21 - 1);
 	seq_printf(m, "%s%d", con->name, con->index);
 	seq_pad(m, ' ');
-	seq_printf(m, "%c%c%c (%s)", con->read ? 'R' : '-',
-			con->write ? 'W' : '-', con->unblank ? 'U' : '-',
-			flags);
+	if (con->flags & CON_NBCON) {
+		if (con->write_atomic || con->write_thread)
+			con_write = 'W';
+	} else {
+		if (con->write)
+			con_write = 'W';
+	}
+	seq_printf(m, "%c%c%c (%s)", con->read ? 'R' : '-', con_write,
+		   con->unblank ? 'U' : '-', flags);
 	if (dev)
 		seq_printf(m, " %4d:%d", MAJOR(dev), MINOR(dev));
 
diff --git a/include/linux/bottom_half.h b/include/linux/bottom_half.h
index fc53e0ad56d90..448bbef474564 100644
--- a/include/linux/bottom_half.h
+++ b/include/linux/bottom_half.h
@@ -35,8 +35,10 @@ static inline void local_bh_enable(void)
 
 #ifdef CONFIG_PREEMPT_RT
 extern bool local_bh_blocked(void);
+extern void softirq_preempt(void);
 #else
 static inline bool local_bh_blocked(void) { return false; }
+static inline void softirq_preempt(void) { }
 #endif
 
 #endif /* _LINUX_BH_H */
diff --git a/include/linux/console.h b/include/linux/console.h
index 779d388af8a0a..ac14ff49e86bb 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -16,7 +16,9 @@
 
 #include <linux/atomic.h>
 #include <linux/bits.h>
+#include <linux/irq_work.h>
 #include <linux/rculist.h>
+#include <linux/rcuwait.h>
 #include <linux/types.h>
 
 struct vc_data;
@@ -303,9 +305,15 @@ struct nbcon_write_context {
  * @node:		hlist node for the console list
  *
  * @write_atomic:	Write callback for atomic context
+ * @write_thread:	Write callback for non-atomic context
+ * @uart_port:		Callback to provide the associated uart port
  * @nbcon_state:	State for nbcon consoles
  * @nbcon_seq:		Sequence number of the next record for nbcon to print
  * @pbufs:		Pointer to nbcon private buffer
+ * @locked_port:	True, if the port lock is locked by nbcon
+ * @kthread:		Printer kthread for this console
+ * @rcuwait:		RCU-safe wait object for @kthread waking
+ * @irq_work:		Defer @kthread waking to IRQ work context
  */
 struct console {
 	char			name[16];
@@ -329,9 +337,16 @@ struct console {
 	/* nbcon console specific members */
 	bool			(*write_atomic)(struct console *con,
 						struct nbcon_write_context *wctxt);
+	bool			(*write_thread)(struct console *con,
+						struct nbcon_write_context *wctxt);
+	struct uart_port *	(*uart_port)(struct console *con);
 	atomic_t		__private nbcon_state;
 	atomic_long_t		__private nbcon_seq;
 	struct printk_buffers	*pbufs;
+	bool			locked_port;
+	struct task_struct	*kthread;
+	struct rcuwait		rcuwait;
+	struct irq_work		irq_work;
 };
 
 #ifdef CONFIG_LOCKDEP
@@ -459,13 +474,19 @@ static inline bool console_is_registered(const struct console *con)
 	hlist_for_each_entry(con, &console_list, node)
 
 #ifdef CONFIG_PRINTK
+extern void nbcon_cpu_emergency_enter(void);
+extern void nbcon_cpu_emergency_exit(void);
 extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt);
 extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt);
 extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt);
+extern void nbcon_reacquire(struct nbcon_write_context *wctxt);
 #else
+static inline void nbcon_cpu_emergency_enter(void) { }
+static inline void nbcon_cpu_emergency_exit(void) { }
 static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return false; }
 static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; }
 static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; }
+static inline void nbcon_reacquire(struct nbcon_write_context *wctxt) { }
 #endif
 
 extern int console_set_on_cmdline;
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index d95ab85f96ba5..8b3ab0cc1334d 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -60,7 +60,7 @@
 #define EXIT_TO_USER_MODE_WORK						\
 	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |		\
 	 _TIF_NEED_RESCHED | _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL |	\
-	 ARCH_EXIT_TO_USER_MODE_WORK)
+	 _TIF_NEED_RESCHED_LAZY | ARCH_EXIT_TO_USER_MODE_WORK)
 
 /**
  * arch_enter_from_user_mode - Architecture specific sanity check for user mode regs
diff --git a/include/linux/entry-kvm.h b/include/linux/entry-kvm.h
index 6813171afccb2..674a622c91be2 100644
--- a/include/linux/entry-kvm.h
+++ b/include/linux/entry-kvm.h
@@ -18,7 +18,7 @@
 
 #define XFER_TO_GUEST_MODE_WORK						\
 	(_TIF_NEED_RESCHED | _TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL |	\
-	 _TIF_NOTIFY_RESUME | ARCH_XFER_TO_GUEST_MODE_WORK)
+	 _TIF_NOTIFY_RESUME | _TIF_NEED_RESCHED_LAZY | ARCH_XFER_TO_GUEST_MODE_WORK)
 
 struct kvm_vcpu;
 
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 76121c2bb4f82..f75f6bc195d18 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -609,6 +609,35 @@ extern void __raise_softirq_irqoff(unsigned int nr);
 extern void raise_softirq_irqoff(unsigned int nr);
 extern void raise_softirq(unsigned int nr);
 
+#ifdef CONFIG_PREEMPT_RT
+DECLARE_PER_CPU(struct task_struct *, timersd);
+DECLARE_PER_CPU(unsigned long, pending_timer_softirq);
+
+extern void raise_timer_softirq(void);
+extern void raise_hrtimer_softirq(void);
+
+static inline unsigned int local_pending_timers(void)
+{
+        return __this_cpu_read(pending_timer_softirq);
+}
+
+#else
+static inline void raise_timer_softirq(void)
+{
+	raise_softirq(TIMER_SOFTIRQ);
+}
+
+static inline void raise_hrtimer_softirq(void)
+{
+	raise_softirq_irqoff(HRTIMER_SOFTIRQ);
+}
+
+static inline unsigned int local_pending_timers(void)
+{
+        return local_softirq_pending();
+}
+#endif
+
 DECLARE_PER_CPU(struct task_struct *, ksoftirqd);
 
 static inline struct task_struct *this_cpu_ksoftirqd(void)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index a16c9cc063fe0..4d06162165e78 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3266,7 +3266,11 @@ struct softnet_data {
 	int			defer_count;
 	int			defer_ipi_scheduled;
 	struct sk_buff		*defer_list;
+#ifndef CONFIG_PREEMPT_RT
 	call_single_data_t	defer_csd;
+#else
+	struct work_struct	defer_work;
+#endif
 };
 
 static inline void input_queue_head_incr(struct softnet_data *sd)
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 9aa6358a1a16b..cd16f0330fba2 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -230,15 +230,21 @@ do { \
 #define preempt_enable() \
 do { \
 	barrier(); \
-	if (unlikely(preempt_count_dec_and_test())) \
+	if (unlikely(preempt_count_dec_and_test())) { \
+		instrumentation_begin(); \
 		__preempt_schedule(); \
+		instrumentation_end(); \
+	} \
 } while (0)
 
 #define preempt_enable_notrace() \
 do { \
 	barrier(); \
-	if (unlikely(__preempt_count_dec_and_test())) \
+	if (unlikely(__preempt_count_dec_and_test())) { \
+		instrumentation_begin(); \
 		__preempt_schedule_notrace(); \
+		instrumentation_end(); \
+	} \
 } while (0)
 
 #define preempt_check_resched() \
diff --git a/include/linux/printk.h b/include/linux/printk.h
index 8ef499ab3c1ed..196a4cf3ccb76 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -9,6 +9,8 @@
 #include <linux/ratelimit_types.h>
 #include <linux/once_lite.h>
 
+struct uart_port;
+
 extern const char linux_banner[];
 extern const char linux_proc_banner[];
 
@@ -159,13 +161,16 @@ __printf(1, 2) __cold int _printk_deferred(const char *fmt, ...);
 
 extern void __printk_safe_enter(void);
 extern void __printk_safe_exit(void);
+extern void __printk_deferred_enter(void);
+extern void __printk_deferred_exit(void);
+
 /*
  * The printk_deferred_enter/exit macros are available only as a hack for
  * some code paths that need to defer all printk console printing. Interrupts
  * must be disabled for the deferred duration.
  */
-#define printk_deferred_enter __printk_safe_enter
-#define printk_deferred_exit __printk_safe_exit
+#define printk_deferred_enter() __printk_deferred_enter()
+#define printk_deferred_exit() __printk_deferred_exit()
 
 /*
  * Please don't use printk_ratelimit(), because it shares ratelimiting state
@@ -192,6 +197,9 @@ void show_regs_print_info(const char *log_lvl);
 extern asmlinkage void dump_stack_lvl(const char *log_lvl) __cold;
 extern asmlinkage void dump_stack(void) __cold;
 void printk_trigger_flush(void);
+extern void nbcon_handle_port_lock(struct uart_port *up);
+extern void nbcon_handle_port_unlock(struct uart_port *up);
+void nbcon_atomic_flush_unsafe(void);
 #else
 static inline __printf(1, 0)
 int vprintk(const char *s, va_list args)
@@ -271,6 +279,19 @@ static inline void dump_stack(void)
 static inline void printk_trigger_flush(void)
 {
 }
+
+static inline void nbcon_handle_port_lock(struct uart_port *up)
+{
+}
+
+static inline void nbcon_handle_port_unlock(struct uart_port *up)
+{
+}
+
+static inline void nbcon_atomic_flush_unsafe(void)
+{
+}
+
 #endif
 
 #ifdef CONFIG_SMP
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index f7206b2623c98..31d523c4e0893 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -301,6 +301,11 @@ static inline void rcu_lock_acquire(struct lockdep_map *map)
 	lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
 }
 
+static inline void rcu_try_lock_acquire(struct lockdep_map *map)
+{
+	lock_acquire(map, 0, 1, 2, 0, NULL, _THIS_IP_);
+}
+
 static inline void rcu_lock_release(struct lockdep_map *map)
 {
 	lock_release(map, _THIS_IP_);
@@ -315,6 +320,7 @@ int rcu_read_lock_any_held(void);
 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 # define rcu_lock_acquire(a)		do { } while (0)
+# define rcu_try_lock_acquire(a)	do { } while (0)
 # define rcu_lock_release(a)		do { } while (0)
 
 static inline int rcu_read_lock_held(void)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 292c316972485..23d2153a90777 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1910,6 +1910,7 @@ static inline int dl_task_check_affinity(struct task_struct *p, const struct cpu
 }
 #endif
 
+extern bool task_is_pi_boosted(const struct task_struct *p);
 extern int yield_to(struct task_struct *p, bool preempt);
 extern void set_user_nice(struct task_struct *p, long nice);
 extern int task_prio(const struct task_struct *p);
@@ -2054,17 +2055,17 @@ static inline void update_tsk_thread_flag(struct task_struct *tsk, int flag,
 	update_ti_thread_flag(task_thread_info(tsk), flag, value);
 }
 
-static inline int test_and_set_tsk_thread_flag(struct task_struct *tsk, int flag)
+static inline bool test_and_set_tsk_thread_flag(struct task_struct *tsk, int flag)
 {
 	return test_and_set_ti_thread_flag(task_thread_info(tsk), flag);
 }
 
-static inline int test_and_clear_tsk_thread_flag(struct task_struct *tsk, int flag)
+static inline bool test_and_clear_tsk_thread_flag(struct task_struct *tsk, int flag)
 {
 	return test_and_clear_ti_thread_flag(task_thread_info(tsk), flag);
 }
 
-static inline int test_tsk_thread_flag(struct task_struct *tsk, int flag)
+static inline bool test_tsk_thread_flag(struct task_struct *tsk, int flag)
 {
 	return test_ti_thread_flag(task_thread_info(tsk), flag);
 }
@@ -2077,9 +2078,11 @@ static inline void set_tsk_need_resched(struct task_struct *tsk)
 static inline void clear_tsk_need_resched(struct task_struct *tsk)
 {
 	clear_tsk_thread_flag(tsk,TIF_NEED_RESCHED);
+	if (IS_ENABLED(CONFIG_PREEMPT_BUILD_AUTO))
+		clear_tsk_thread_flag(tsk, TIF_NEED_RESCHED_LAZY);
 }
 
-static inline int test_tsk_need_resched(struct task_struct *tsk)
+static inline bool test_tsk_need_resched(struct task_struct *tsk)
 {
 	return unlikely(test_tsk_thread_flag(tsk,TIF_NEED_RESCHED));
 }
@@ -2260,7 +2263,7 @@ static inline int rwlock_needbreak(rwlock_t *lock)
 
 static __always_inline bool need_resched(void)
 {
-	return unlikely(tif_need_resched());
+	return unlikely(tif_need_resched_lazy() || tif_need_resched());
 }
 
 /*
diff --git a/include/linux/sched/idle.h b/include/linux/sched/idle.h
index 478084f9105e1..719416fe8ddc0 100644
--- a/include/linux/sched/idle.h
+++ b/include/linux/sched/idle.h
@@ -63,7 +63,7 @@ static __always_inline bool __must_check current_set_polling_and_test(void)
 	 */
 	smp_mb__after_atomic();
 
-	return unlikely(tif_need_resched());
+	return unlikely(need_resched());
 }
 
 static __always_inline bool __must_check current_clr_polling_and_test(void)
@@ -76,7 +76,7 @@ static __always_inline bool __must_check current_clr_polling_and_test(void)
 	 */
 	smp_mb__after_atomic();
 
-	return unlikely(tif_need_resched());
+	return unlikely(need_resched());
 }
 
 #else
@@ -85,11 +85,11 @@ static inline void __current_clr_polling(void) { }
 
 static inline bool __must_check current_set_polling_and_test(void)
 {
-	return unlikely(tif_need_resched());
+	return unlikely(need_resched());
 }
 static inline bool __must_check current_clr_polling_and_test(void)
 {
-	return unlikely(tif_need_resched());
+	return unlikely(need_resched());
 }
 #endif
 
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index be65de65fe612..ec46e3b49ee99 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -153,6 +153,8 @@ struct uart_8250_port {
 #define MSR_SAVE_FLAGS UART_MSR_ANY_DELTA
 	unsigned char		msr_saved_flags;
 
+	bool			console_newline_needed;
+
 	struct uart_8250_dma	*dma;
 	const struct uart_8250_ops *ops;
 
@@ -204,6 +206,10 @@ void serial8250_init_port(struct uart_8250_port *up);
 void serial8250_set_defaults(struct uart_8250_port *up);
 void serial8250_console_write(struct uart_8250_port *up, const char *s,
 			      unsigned int count);
+bool serial8250_console_write_atomic(struct uart_8250_port *up,
+				     struct nbcon_write_context *wctxt);
+bool serial8250_console_write_thread(struct uart_8250_port *up,
+				     struct nbcon_write_context *wctxt);
 int serial8250_console_setup(struct uart_port *port, char *options, bool probe);
 int serial8250_console_exit(struct uart_port *port);
 
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 89f7b6c63598c..198d8088a9984 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -595,6 +595,7 @@ struct uart_port {
 static inline void uart_port_lock(struct uart_port *up)
 {
 	spin_lock(&up->lock);
+	nbcon_handle_port_lock(up);
 }
 
 /**
@@ -604,6 +605,7 @@ static inline void uart_port_lock(struct uart_port *up)
 static inline void uart_port_lock_irq(struct uart_port *up)
 {
 	spin_lock_irq(&up->lock);
+	nbcon_handle_port_lock(up);
 }
 
 /**
@@ -614,6 +616,7 @@ static inline void uart_port_lock_irq(struct uart_port *up)
 static inline void uart_port_lock_irqsave(struct uart_port *up, unsigned long *flags)
 {
 	spin_lock_irqsave(&up->lock, *flags);
+	nbcon_handle_port_lock(up);
 }
 
 /**
@@ -624,7 +627,11 @@ static inline void uart_port_lock_irqsave(struct uart_port *up, unsigned long *f
  */
 static inline bool uart_port_trylock(struct uart_port *up)
 {
-	return spin_trylock(&up->lock);
+	if (!spin_trylock(&up->lock))
+		return false;
+
+	nbcon_handle_port_lock(up);
+	return true;
 }
 
 /**
@@ -636,7 +643,11 @@ static inline bool uart_port_trylock(struct uart_port *up)
  */
 static inline bool uart_port_trylock_irqsave(struct uart_port *up, unsigned long *flags)
 {
-	return spin_trylock_irqsave(&up->lock, *flags);
+	if (!spin_trylock_irqsave(&up->lock, *flags))
+		return false;
+
+	nbcon_handle_port_lock(up);
+	return true;
 }
 
 /**
@@ -645,6 +656,7 @@ static inline bool uart_port_trylock_irqsave(struct uart_port *up, unsigned long
  */
 static inline void uart_port_unlock(struct uart_port *up)
 {
+	nbcon_handle_port_unlock(up);
 	spin_unlock(&up->lock);
 }
 
@@ -654,6 +666,7 @@ static inline void uart_port_unlock(struct uart_port *up)
  */
 static inline void uart_port_unlock_irq(struct uart_port *up)
 {
+	nbcon_handle_port_unlock(up);
 	spin_unlock_irq(&up->lock);
 }
 
@@ -664,6 +677,7 @@ static inline void uart_port_unlock_irq(struct uart_port *up)
  */
 static inline void uart_port_unlock_irqrestore(struct uart_port *up, unsigned long flags)
 {
+	nbcon_handle_port_unlock(up);
 	spin_unlock_irqrestore(&up->lock, flags);
 }
 
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 127ef3b2e6073..236610e4a8fa5 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -229,7 +229,7 @@ static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp
 
 	srcu_check_nmi_safety(ssp, true);
 	retval = __srcu_read_lock_nmisafe(ssp);
-	rcu_lock_acquire(&ssp->dep_map);
+	rcu_try_lock_acquire(&ssp->dep_map);
 	return retval;
 }
 
diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index 9ea0b28068f49..5ded1450ac1a1 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -59,6 +59,16 @@ enum syscall_work_bit {
 
 #include <asm/thread_info.h>
 
+#ifdef CONFIG_PREEMPT_BUILD_AUTO
+# define TIF_NEED_RESCHED_LAZY		TIF_ARCH_RESCHED_LAZY
+# define _TIF_NEED_RESCHED_LAZY		_TIF_ARCH_RESCHED_LAZY
+# define TIF_NEED_RESCHED_LAZY_OFFSET	(TIF_NEED_RESCHED_LAZY - TIF_NEED_RESCHED)
+#else
+# define TIF_NEED_RESCHED_LAZY		TIF_NEED_RESCHED
+# define _TIF_NEED_RESCHED_LAZY		_TIF_NEED_RESCHED
+# define TIF_NEED_RESCHED_LAZY_OFFSET	0
+#endif
+
 #ifdef __KERNEL__
 
 #ifndef arch_set_restart_data
@@ -185,6 +195,13 @@ static __always_inline bool tif_need_resched(void)
 			     (unsigned long *)(&current_thread_info()->flags));
 }
 
+static __always_inline bool tif_need_resched_lazy(void)
+{
+	return IS_ENABLED(CONFIG_PREEMPT_BUILD_AUTO) &&
+		arch_test_bit(TIF_NEED_RESCHED_LAZY,
+			      (unsigned long *)(&current_thread_info()->flags));
+}
+
 #else
 
 static __always_inline bool tif_need_resched(void)
@@ -193,6 +210,13 @@ static __always_inline bool tif_need_resched(void)
 			(unsigned long *)(&current_thread_info()->flags));
 }
 
+static __always_inline bool tif_need_resched_lazy(void)
+{
+	return IS_ENABLED(CONFIG_PREEMPT_BUILD_AUTO) &&
+		test_bit(TIF_NEED_RESCHED_LAZY,
+			 (unsigned long *)(&current_thread_info()->flags));
+}
+
 #endif /* _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H */
 
 #ifndef CONFIG_HAVE_ARCH_WITHIN_STACK_FRAMES
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index d68ff9b1247f9..0681b3d5a85c6 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -178,8 +178,8 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status);
 
 enum trace_flag_type {
 	TRACE_FLAG_IRQS_OFF		= 0x01,
-	TRACE_FLAG_IRQS_NOSUPPORT	= 0x02,
-	TRACE_FLAG_NEED_RESCHED		= 0x04,
+	TRACE_FLAG_NEED_RESCHED		= 0x02,
+	TRACE_FLAG_NEED_RESCHED_LAZY	= 0x04,
 	TRACE_FLAG_HARDIRQ		= 0x08,
 	TRACE_FLAG_SOFTIRQ		= 0x10,
 	TRACE_FLAG_PREEMPT_RESCHED	= 0x20,
@@ -205,11 +205,11 @@ static inline unsigned int tracing_gen_ctx(void)
 
 static inline unsigned int tracing_gen_ctx_flags(unsigned long irqflags)
 {
-	return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT);
+	return tracing_gen_ctx_irq_test(0);
 }
 static inline unsigned int tracing_gen_ctx(void)
 {
-	return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT);
+	return tracing_gen_ctx_irq_test(0);
 }
 #endif
 
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index c2f1fd95a8214..0f3d4c2a41cb7 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -11,6 +11,13 @@ config PREEMPT_BUILD
 	select PREEMPTION
 	select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
 
+config PREEMPT_BUILD_AUTO
+	bool
+	select PREEMPT_BUILD
+
+config HAVE_PREEMPT_AUTO
+	bool
+
 choice
 	prompt "Preemption Model"
 	default PREEMPT_NONE
@@ -67,9 +74,17 @@ config PREEMPT
 	  embedded system with latency requirements in the milliseconds
 	  range.
 
+config PREEMPT_AUTO
+	bool "Automagic preemption mode with runtime tweaking support"
+	depends on HAVE_PREEMPT_AUTO
+	select PREEMPT_BUILD_AUTO
+	help
+	  Add some sensible blurb here
+
 config PREEMPT_RT
 	bool "Fully Preemptible Kernel (Real-Time)"
 	depends on EXPERT && ARCH_SUPPORTS_RT
+	select PREEMPT_BUILD_AUTO if HAVE_PREEMPT_AUTO
 	select PREEMPTION
 	help
 	  This option turns the kernel into a real-time kernel by replacing
@@ -95,7 +110,7 @@ config PREEMPTION
 
 config PREEMPT_DYNAMIC
 	bool "Preemption behaviour defined on boot"
-	depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT
+	depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT && !PREEMPT_AUTO
 	select JUMP_LABEL if HAVE_PREEMPT_DYNAMIC_KEY
 	select PREEMPT_BUILD
 	default y if HAVE_PREEMPT_DYNAMIC_CALL
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index d7ee4bc3f2ba3..c1f706038637c 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -155,7 +155,7 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
 
 		local_irq_enable_exit_to_user(ti_work);
 
-		if (ti_work & _TIF_NEED_RESCHED)
+		if (ti_work & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY))
 			schedule();
 
 		if (ti_work & _TIF_UPROBE)
@@ -385,7 +385,7 @@ void raw_irqentry_exit_cond_resched(void)
 		rcu_irq_exit_check_preempt();
 		if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
 			WARN_ON_ONCE(!on_thread_stack());
-		if (need_resched())
+		if (test_tsk_need_resched(current))
 			preempt_schedule_irq();
 	}
 }
diff --git a/kernel/entry/kvm.c b/kernel/entry/kvm.c
index 2e0f75bcb7fd1..d952fa5ee8801 100644
--- a/kernel/entry/kvm.c
+++ b/kernel/entry/kvm.c
@@ -13,7 +13,7 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
 			return -EINTR;
 		}
 
-		if (ti_work & _TIF_NEED_RESCHED)
+		if (ti_work & (_TIF_NEED_RESCHED | TIF_NEED_RESCHED_LAZY))
 			schedule();
 
 		if (ti_work & _TIF_NOTIFY_RESUME)
diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index 1d4bc493b2f4b..486c68c11bbe2 100644
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -179,6 +179,15 @@ KERNEL_ATTR_RO(crash_elfcorehdr_size);
 
 #endif /* CONFIG_CRASH_CORE */
 
+#if defined(CONFIG_PREEMPT_RT)
+static ssize_t realtime_show(struct kobject *kobj,
+			     struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%d\n", 1);
+}
+KERNEL_ATTR_RO(realtime);
+#endif
+
 /* whether file capabilities are enabled */
 static ssize_t fscaps_show(struct kobject *kobj,
 				  struct kobj_attribute *attr, char *buf)
@@ -274,6 +283,9 @@ static struct attribute * kernel_attrs[] = {
 #ifndef CONFIG_TINY_RCU
 	&rcu_expedited_attr.attr,
 	&rcu_normal_attr.attr,
+#endif
+#ifdef CONFIG_PREEMPT_RT
+	&realtime_attr.attr,
 #endif
 	NULL
 };
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index e85b5ad3e2069..00465373d358f 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -56,6 +56,7 @@
 #include <linux/kprobes.h>
 #include <linux/lockdep.h>
 #include <linux/context_tracking.h>
+#include <linux/console.h>
 
 #include <asm/sections.h>
 
@@ -3970,6 +3971,8 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this,
 	if (!debug_locks_off() || debug_locks_silent)
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	pr_warn("\n");
 	pr_warn("================================\n");
 	pr_warn("WARNING: inconsistent lock state\n");
@@ -3998,6 +4001,8 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this,
 
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+
+	nbcon_cpu_emergency_exit();
 }
 
 /*
diff --git a/kernel/panic.c b/kernel/panic.c
index 2807639aab51d..88902355600f5 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -446,6 +446,9 @@ void panic(const char *fmt, ...)
 
 	/* Do not scroll important messages printed above */
 	suppress_printk = 1;
+
+	nbcon_atomic_flush_unsafe();
+
 	local_irq_enable();
 	for (i = 0; ; i += PANIC_TIMER_STEP) {
 		touch_softlockup_watchdog();
@@ -623,6 +626,7 @@ bool oops_may_print(void)
  */
 void oops_enter(void)
 {
+	nbcon_cpu_emergency_enter();
 	tracing_off();
 	/* can't trust the integrity of the kernel anymore: */
 	debug_locks_off();
@@ -645,6 +649,7 @@ void oops_exit(void)
 {
 	do_oops_enter_exit();
 	print_oops_end_marker();
+	nbcon_cpu_emergency_exit();
 	kmsg_dump(KMSG_DUMP_OOPS);
 }
 
@@ -656,6 +661,8 @@ struct warn_args {
 void __warn(const char *file, int line, void *caller, unsigned taint,
 	    struct pt_regs *regs, struct warn_args *args)
 {
+	nbcon_cpu_emergency_enter();
+
 	disable_trace_on_warning();
 
 	if (file)
@@ -686,6 +693,8 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
 
 	/* Just a warning, don't kill lockdep. */
 	add_taint(taint, LOCKDEP_STILL_OK);
+
+	nbcon_cpu_emergency_exit();
 }
 
 #ifdef CONFIG_BUG
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 6c2afee5ef620..a3ae0710346cd 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -44,6 +44,17 @@ enum printk_info_flags {
 };
 
 extern struct printk_ringbuffer *prb;
+extern bool printk_threads_enabled;
+extern bool have_legacy_console;
+extern bool have_boot_console;
+
+/*
+ * Specifies if the console lock/unlock dance is needed for console
+ * printing. If @have_boot_console is true, the nbcon consoles will
+ * be printed serially along with the legacy consoles because nbcon
+ * consoles cannot print simultaneously with boot consoles.
+ */
+#define printing_via_unlock (have_legacy_console || have_boot_console)
 
 __printf(4, 0)
 int vprintk_store(int facility, int level,
@@ -77,6 +88,70 @@ void nbcon_seq_force(struct console *con, u64 seq);
 bool nbcon_alloc(struct console *con);
 void nbcon_init(struct console *con);
 void nbcon_free(struct console *con);
+enum nbcon_prio nbcon_get_default_prio(void);
+void nbcon_atomic_flush_all(void);
+bool nbcon_atomic_emit_next_record(struct console *con);
+void nbcon_kthread_create(struct console *con);
+void nbcon_wake_threads(void);
+void nbcon_legacy_kthread_create(void);
+
+/*
+ * Check if the given console is currently capable and allowed to print
+ * records. Note that this function does not consider the current context,
+ * which can also play a role in deciding if @con can be used to print
+ * records.
+ */
+static inline bool console_is_usable(struct console *con, short flags, bool use_atomic)
+{
+	if (!(flags & CON_ENABLED))
+		return false;
+
+	if ((flags & CON_SUSPENDED))
+		return false;
+
+	if (flags & CON_NBCON) {
+		if (use_atomic) {
+			if (!con->write_atomic)
+				return false;
+		} else {
+			if (!con->write_thread || !con->kthread)
+				return false;
+		}
+	} else {
+		if (!con->write)
+			return false;
+	}
+
+	/*
+	 * Console drivers may assume that per-cpu resources have been
+	 * allocated. So unless they're explicitly marked as being able to
+	 * cope (CON_ANYTIME) don't call them until this CPU is officially up.
+	 */
+	if (!cpu_online(raw_smp_processor_id()) && !(flags & CON_ANYTIME))
+		return false;
+
+	return true;
+}
+
+/**
+ * nbcon_kthread_wake - Wake up a printk thread
+ * @con:        Console to operate on
+ */
+static inline void nbcon_kthread_wake(struct console *con)
+{
+	/*
+	 * Guarantee any new records can be seen by tasks preparing to wait
+	 * before this context checks if the rcuwait is empty.
+	 *
+	 * The full memory barrier in rcuwait_wake_up()  pairs with the full
+	 * memory barrier within set_current_state() of
+	 * ___rcuwait_wait_event(), which is called after prepare_to_rcuwait()
+	 * adds the waiter but before it has checked the wait condition.
+	 *
+	 * This pairs with nbcon_kthread_func:A.
+	 */
+	rcuwait_wake_up(&con->rcuwait); /* LMM(nbcon_kthread_wake:A) */
+}
 
 #else
 
@@ -84,6 +159,11 @@ void nbcon_free(struct console *con);
 #define PRINTK_MESSAGE_MAX	0
 #define PRINTKRB_RECORD_MAX	0
 
+static inline void nbcon_kthread_wake(struct console *con) { }
+static inline void nbcon_kthread_create(struct console *con) { }
+#define printk_threads_enabled (false)
+#define printing_via_unlock (false)
+
 /*
  * In !PRINTK builds we still export console_sem
  * semaphore and some of console functions (console_unlock()/etc.), so
@@ -98,6 +178,11 @@ static inline void nbcon_seq_force(struct console *con, u64 seq) { }
 static inline bool nbcon_alloc(struct console *con) { return false; }
 static inline void nbcon_init(struct console *con) { }
 static inline void nbcon_free(struct console *con) { }
+static inline enum nbcon_prio nbcon_get_default_prio(void) { return NBCON_PRIO_NONE; }
+static inline void nbcon_atomic_flush_all(void) { }
+static bool nbcon_atomic_emit_next_record(struct console *con) { return false; }
+
+static inline bool console_is_usable(struct console *con, short flags, bool use_atomic) { return false; }
 
 #endif /* CONFIG_PRINTK */
 
@@ -130,6 +215,7 @@ struct printk_message {
 };
 
 bool other_cpu_in_panic(void);
+bool this_cpu_in_panic(void);
 bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
 			     bool is_extended, bool may_supress);
 
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index b96077152f49d..a9be219673dbf 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -5,7 +5,11 @@
 #include <linux/kernel.h>
 #include <linux/console.h>
 #include <linux/delay.h>
+#include <linux/kthread.h>
 #include <linux/slab.h>
+#include <linux/serial_core.h>
+#include <linux/syscore_ops.h>
+#include "printk_ringbuffer.h"
 #include "internal.h"
 /*
  * Printk console printing implementation for consoles which does not depend
@@ -210,6 +214,11 @@ void nbcon_seq_force(struct console *con, u64 seq)
 	con->seq = 0;
 }
 
+static void nbcon_context_seq_set(struct nbcon_context *ctxt)
+{
+	ctxt->seq = nbcon_seq_read(ctxt->console);
+}
+
 /**
  * nbcon_seq_try_update - Try to update the console sequence number
  * @ctxt:	Pointer to an acquire context that contains
@@ -234,6 +243,8 @@ static void nbcon_seq_try_update(struct nbcon_context *ctxt, u64 new_seq)
 	}
 }
 
+bool printk_threads_enabled __ro_after_init;
+
 /**
  * nbcon_context_try_acquire_direct - Try to acquire directly
  * @ctxt:	The context of the caller
@@ -571,7 +582,6 @@ static struct printk_buffers panic_nbcon_pbufs;
  * in an unsafe state. Otherwise, on success the caller may assume
  * the console is not in an unsafe state.
  */
-__maybe_unused
 static bool nbcon_context_try_acquire(struct nbcon_context *ctxt)
 {
 	unsigned int cpu = smp_processor_id();
@@ -857,9 +867,26 @@ bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt)
 }
 EXPORT_SYMBOL_GPL(nbcon_exit_unsafe);
 
+void nbcon_reacquire(struct nbcon_write_context *wctxt)
+{
+	struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
+	struct console *con = ctxt->console;
+	struct nbcon_state cur;
+
+	while (!nbcon_context_try_acquire(ctxt))
+		cpu_relax();
+
+	wctxt->outbuf = NULL;
+	wctxt->len = 0;
+	nbcon_state_read(con, &cur);
+	wctxt->unsafe_takeover = cur.unsafe_takeover;
+}
+EXPORT_SYMBOL_GPL(nbcon_reacquire);
+
 /**
  * nbcon_emit_next_record - Emit a record in the acquired context
  * @wctxt:	The write context that will be handed to the write function
+ * @use_atomic:	True if the write_atomic callback is to be used
  *
  * Return:	True if this context still owns the console. False if
  *		ownership was handed over or taken.
@@ -873,8 +900,7 @@ EXPORT_SYMBOL_GPL(nbcon_exit_unsafe);
  * When true is returned, @wctxt->ctxt.backlog indicates whether there are
  * still records pending in the ringbuffer,
  */
-__maybe_unused
-static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt)
+static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt, bool use_atomic)
 {
 	struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
 	struct console *con = ctxt->console;
@@ -924,17 +950,29 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt)
 	nbcon_state_read(con, &cur);
 	wctxt->unsafe_takeover = cur.unsafe_takeover;
 
-	if (con->write_atomic) {
+	if (use_atomic &&
+	    con->write_atomic) {
 		done = con->write_atomic(con, wctxt);
+
+	} else if (!use_atomic &&
+		   con->write_thread &&
+		   con->kthread) {
+		WARN_ON_ONCE(con->kthread != current);
+		done = con->write_thread(con, wctxt);
+
 	} else {
-		nbcon_context_release(ctxt);
 		WARN_ON_ONCE(1);
 		done = false;
 	}
 
-	/* If not done, the emit was aborted. */
-	if (!done)
+	if (!done) {
+		/*
+		 * The emit was aborted. This may have been due to a loss
+		 * of ownership. Explicitly release ownership to be sure.
+		 */
+		nbcon_context_release(ctxt);
 		return false;
+	}
 
 	/*
 	 * Since any dropped message was successfully output, reset the
@@ -961,6 +999,517 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt)
 	return nbcon_context_exit_unsafe(ctxt);
 }
 
+/**
+ * nbcon_kthread_should_wakeup - Check whether a printer thread should wakeup
+ * @con:	Console to operate on
+ * @ctxt:	The acquire context that contains the state
+ *		at console_acquire()
+ *
+ * Return:	True if the thread should shutdown or if the console is
+ *		allowed to print and a record is available. False otherwise.
+ *
+ * After the thread wakes up, it must first check if it should shutdown before
+ * attempting any printing.
+ */
+static bool nbcon_kthread_should_wakeup(struct console *con, struct nbcon_context *ctxt)
+{
+	struct nbcon_state cur;
+	bool is_usable;
+	short flags;
+	int cookie;
+
+	do {
+		if (kthread_should_stop())
+			return true;
+
+		cookie = console_srcu_read_lock();
+		flags = console_srcu_read_flags(con);
+		is_usable = console_is_usable(con, flags, false);
+		console_srcu_read_unlock(cookie);
+
+		if (!is_usable)
+			return false;
+
+		nbcon_state_read(con, &cur);
+
+		/*
+		 * Some other CPU is using the console. Patiently poll
+		 * to see if it becomes available. This is more efficient
+		 * than having every release trigger an irq_work to wake
+		 * the kthread.
+		 */
+		msleep(1);
+	} while (cur.prio != NBCON_PRIO_NONE);
+
+	/* Bring the sequence in @ctxt up to date */
+	nbcon_context_seq_set(ctxt);
+
+	return prb_read_valid(prb, ctxt->seq, NULL);
+}
+
+/**
+ * nbcon_kthread_func - The printer thread function
+ * @__console:	Console to operate on
+ */
+static int nbcon_kthread_func(void *__console)
+{
+	struct console *con = __console;
+	struct nbcon_write_context wctxt = {
+		.ctxt.console	= con,
+		.ctxt.prio	= NBCON_PRIO_NORMAL,
+	};
+	struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt);
+	struct uart_port *port = NULL;
+	unsigned long flags;
+	short con_flags;
+	bool backlog;
+	int cookie;
+	int ret;
+
+	if (con->uart_port)
+		port = con->uart_port(con);
+
+wait_for_event:
+	/*
+	 * Guarantee this task is visible on the rcuwait before
+	 * checking the wake condition.
+	 *
+	 * The full memory barrier within set_current_state() of
+	 * ___rcuwait_wait_event() pairs with the full memory
+	 * barrier within rcuwait_has_sleeper().
+	 *
+	 * This pairs with rcuwait_has_sleeper:A and nbcon_kthread_wake:A.
+	 */
+	ret = rcuwait_wait_event(&con->rcuwait,
+				 nbcon_kthread_should_wakeup(con, ctxt),
+				 TASK_INTERRUPTIBLE); /* LMM(nbcon_kthread_func:A) */
+
+	if (kthread_should_stop())
+		return 0;
+
+	/* Wait was interrupted by a spurious signal, go back to sleep. */
+	if (ret)
+		goto wait_for_event;
+
+	do {
+		backlog = false;
+
+		cookie = console_srcu_read_lock();
+
+		con_flags = console_srcu_read_flags(con);
+
+		if (console_is_usable(con, con_flags, false)) {
+			/*
+			 * Ensure this stays on the CPU to make handover and
+			 * takeover possible.
+			 */
+			if (port)
+				spin_lock_irqsave(&port->lock, flags);
+			else
+				migrate_disable();
+
+			if (nbcon_context_try_acquire(ctxt)) {
+				/*
+				 * If the emit fails, this context is no
+				 * longer the owner.
+				 */
+				if (nbcon_emit_next_record(&wctxt, false)) {
+					nbcon_context_release(ctxt);
+					backlog = ctxt->backlog;
+				}
+			}
+
+			if (port)
+				spin_unlock_irqrestore(&port->lock, flags);
+			else
+				migrate_enable();
+		}
+
+		console_srcu_read_unlock(cookie);
+
+		cond_resched();
+
+	} while (backlog);
+
+	goto wait_for_event;
+}
+
+/**
+ * nbcon_irq_work - irq work to wake printk thread
+ * @irq_work:	The irq work to operate on
+ */
+static void nbcon_irq_work(struct irq_work *irq_work)
+{
+	struct console *con = container_of(irq_work, struct console, irq_work);
+
+	nbcon_kthread_wake(con);
+}
+
+static inline bool rcuwait_has_sleeper(struct rcuwait *w)
+{
+	bool has_sleeper;
+
+	rcu_read_lock();
+	/*
+	 * Guarantee any new records can be seen by tasks preparing to wait
+	 * before this context checks if the rcuwait is empty.
+	 *
+	 * This full memory barrier pairs with the full memory barrier within
+	 * set_current_state() of ___rcuwait_wait_event(), which is called
+	 * after prepare_to_rcuwait() adds the waiter but before it has
+	 * checked the wait condition.
+	 *
+	 * This pairs with nbcon_kthread_func:A.
+	 */
+	smp_mb(); /* LMM(rcuwait_has_sleeper:A) */
+	has_sleeper = !!rcu_dereference(w->task);
+	rcu_read_unlock();
+
+	return has_sleeper;
+}
+
+/**
+ * nbcon_wake_threads - Wake up printing threads using irq_work
+ */
+void nbcon_wake_threads(void)
+{
+	struct console *con;
+	int cookie;
+
+	cookie = console_srcu_read_lock();
+	for_each_console_srcu(con) {
+		/*
+		 * Only schedule irq_work if the printing thread is
+		 * actively waiting. If not waiting, the thread will
+		 * notice by itself that it has work to do.
+		 */
+		if (con->kthread && rcuwait_has_sleeper(&con->rcuwait))
+			irq_work_queue(&con->irq_work);
+	}
+	console_srcu_read_unlock(cookie);
+}
+
+/* Track the nbcon emergency nesting per CPU. */
+static DEFINE_PER_CPU(unsigned int, nbcon_pcpu_emergency_nesting);
+static unsigned int early_nbcon_pcpu_emergency_nesting __initdata;
+
+/**
+ * nbcon_get_cpu_emergency_nesting - Get the per CPU emergency nesting pointer
+ *
+ * Return:	Either a pointer to the per CPU emergency nesting counter of
+ *		the current CPU or to the init data during early boot.
+ */
+static __ref unsigned int *nbcon_get_cpu_emergency_nesting(void)
+{
+	/*
+	 * The value of __printk_percpu_data_ready gets set in normal
+	 * context and before SMP initialization. As a result it could
+	 * never change while inside an nbcon emergency section.
+	 */
+	if (!printk_percpu_data_ready())
+		return &early_nbcon_pcpu_emergency_nesting;
+
+	return this_cpu_ptr(&nbcon_pcpu_emergency_nesting);
+}
+
+/**
+ * nbcon_atomic_emit_one - Print one record for an nbcon console using the
+ *					write_atomic() callback
+ * @wctxt:			An initialized write context struct to use
+ *				for this context
+ *
+ * Return:	False if the given console could not print a record or there
+ *		are no more records to print, otherwise true.
+ *
+ * This is an internal helper to handle the locking of the console before
+ * calling nbcon_emit_next_record().
+ */
+static bool nbcon_atomic_emit_one(struct nbcon_write_context *wctxt)
+{
+	struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
+
+	if (!nbcon_context_try_acquire(ctxt))
+		return false;
+
+	/*
+	 * nbcon_emit_next_record() returns false when the console was
+	 * handed over or taken over. In both cases the context is no
+	 * longer valid.
+	 */
+	if (!nbcon_emit_next_record(wctxt, true))
+		return false;
+
+	nbcon_context_release(ctxt);
+
+	return ctxt->backlog;
+}
+
+/**
+ * nbcon_get_default_prio - The appropriate nbcon priority to use for nbcon
+ *				printing on the current CPU
+ *
+ * Return:	The nbcon_prio to use for acquiring an nbcon console in this
+ *		context for printing.
+ */
+enum nbcon_prio nbcon_get_default_prio(void)
+{
+	unsigned int *cpu_emergency_nesting;
+
+	if (this_cpu_in_panic())
+		return NBCON_PRIO_PANIC;
+
+	cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting();
+	if (*cpu_emergency_nesting)
+		return NBCON_PRIO_EMERGENCY;
+
+	return NBCON_PRIO_NORMAL;
+}
+
+/**
+ * nbcon_atomic_emit_next_record - Print one record for an nbcon console
+ *					using the write_atomic() callback
+ * @con:	The console to print on
+ *
+ * Return:	True if a record could be printed, otherwise false.
+ * Context:	Any context which could not be migrated to another CPU.
+ *
+ * This function is meant to be called by console_flush_all() to print records
+ * on nbcon consoles using the write_atomic() callback. Essentially it is the
+ * nbcon version of console_emit_next_record().
+ */
+bool nbcon_atomic_emit_next_record(struct console *con)
+{
+	struct uart_port *port = con->uart_port(con);
+	static DEFINE_SPINLOCK(shared_spinlock);
+	bool progress = false;
+	enum nbcon_prio prio;
+	unsigned long flags;
+
+	/*
+	 * If there is no port lock available, fallback to a shared
+	 * spinlock. This serves to provide the necessary type of
+	 * migration/preemption disabling while printing.
+	 */
+	if (port)
+		spin_lock_irqsave(&port->lock, flags);
+	else
+		spin_lock_irqsave(&shared_spinlock, flags);
+
+	/*
+	 * Do not emit for EMERGENCY priority. The console will be
+	 * explicitly flushed when exiting the emergency section.
+	 */
+	prio = nbcon_get_default_prio();
+	if (prio != NBCON_PRIO_EMERGENCY) {
+		struct nbcon_write_context wctxt = { };
+		struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt);
+
+		ctxt->console	= con;
+		ctxt->prio	= prio;
+
+		progress = nbcon_atomic_emit_one(&wctxt);
+	}
+
+	if (port)
+		spin_unlock_irqrestore(&port->lock, flags);
+	else
+		spin_unlock_irqrestore(&shared_spinlock, flags);
+
+	return progress;
+}
+
+/**
+ * __nbcon_atomic_flush_all - Flush all nbcon consoles using their
+ *					write_atomic() callback
+ * @stop_seq:			Flush up until this record
+ * @allow_unsafe_takeover:	True, to allow unsafe hostile takeovers
+ */
+static void __nbcon_atomic_flush_all(u64 stop_seq, bool allow_unsafe_takeover)
+{
+	struct nbcon_write_context wctxt = { };
+	struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt);
+	enum nbcon_prio prio = nbcon_get_default_prio();
+	struct console *con;
+	bool any_progress;
+	int cookie;
+
+	do {
+		any_progress = false;
+
+		cookie = console_srcu_read_lock();
+		for_each_console_srcu(con) {
+			short flags = console_srcu_read_flags(con);
+
+			if (!(flags & CON_NBCON))
+				continue;
+
+			if (!console_is_usable(con, flags, true))
+				continue;
+
+			if (nbcon_seq_read(con) >= stop_seq)
+				continue;
+
+			memset(ctxt, 0, sizeof(*ctxt));
+			ctxt->console			= con;
+			ctxt->spinwait_max_us		= 2000;
+			ctxt->prio			= prio;
+			ctxt->allow_unsafe_takeover	= allow_unsafe_takeover;
+
+			any_progress |= nbcon_atomic_emit_one(&wctxt);
+		}
+		console_srcu_read_unlock(cookie);
+	} while (any_progress);
+}
+
+/**
+ * nbcon_atomic_flush_all - Flush all nbcon consoles using their
+ *				write_atomic() callback
+ *
+ * Flush the backlog up through the currently newest record. Any new
+ * records added while flushing will not be flushed. This is to avoid
+ * one CPU printing unbounded because other CPUs continue to add records.
+ *
+ * Context:	Any context which could not be migrated to another CPU.
+ */
+void nbcon_atomic_flush_all(void)
+{
+	__nbcon_atomic_flush_all(prb_next_reserve_seq(prb), false);
+}
+
+/**
+ * nbcon_atomic_flush_unsafe - Flush all nbcon consoles using their
+ *	write_atomic() callback and allowing unsafe hostile takeovers
+ *
+ * Flush the backlog up through the currently newest record. Unsafe hostile
+ * takeovers will be performed, if necessary.
+ *
+ * Context:	Any context which could not be migrated to another CPU.
+ */
+void nbcon_atomic_flush_unsafe(void)
+{
+	__nbcon_atomic_flush_all(prb_next_reserve_seq(prb), true);
+}
+
+/**
+ * nbcon_cpu_emergency_enter - Enter an emergency section where printk()
+ *	messages for that CPU are only stored
+ *
+ * Upon exiting the emergency section, all stored messages are flushed.
+ *
+ * Context:	Any context. Disables preemption.
+ *
+ * When within an emergency section, no printing occurs on that CPU. This
+ * is to allow all emergency messages to be dumped into the ringbuffer before
+ * flushing the ringbuffer. The actual printing occurs when exiting the
+ * outermost emergency section.
+ */
+void nbcon_cpu_emergency_enter(void)
+{
+	unsigned int *cpu_emergency_nesting;
+
+	preempt_disable();
+
+	cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting();
+	(*cpu_emergency_nesting)++;
+}
+
+/**
+ * nbcon_cpu_emergency_exit - Exit an emergency section and flush the
+ *	stored messages
+ *
+ * Flushing only occurs when exiting all nesting for the CPU.
+ *
+ * Context:	Any context. Enables preemption.
+ */
+void nbcon_cpu_emergency_exit(void)
+{
+	unsigned int *cpu_emergency_nesting;
+
+	cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting();
+
+	WARN_ON_ONCE(*cpu_emergency_nesting == 0);
+
+	if (*cpu_emergency_nesting == 1)
+		printk_trigger_flush();
+
+	/* Undo the nesting count of nbcon_cpu_emergency_enter(). */
+	(*cpu_emergency_nesting)--;
+
+	preempt_enable();
+}
+
+/**
+ * nbcon_kthread_stop - Stop a printer thread
+ * @con:	Console to operate on
+ */
+static void nbcon_kthread_stop(struct console *con)
+{
+	lockdep_assert_console_list_lock_held();
+
+	if (!con->kthread)
+		return;
+
+	kthread_stop(con->kthread);
+	con->kthread = NULL;
+}
+
+/**
+ * nbcon_kthread_create - Create a printer thread
+ * @con:	Console to operate on
+ *
+ * If it fails, let the console proceed. The atomic part might
+ * be usable and useful.
+ */
+void nbcon_kthread_create(struct console *con)
+{
+	struct task_struct *kt;
+
+	lockdep_assert_console_list_lock_held();
+
+	if (!(con->flags & CON_NBCON) || !con->write_thread)
+		return;
+
+	if (!printk_threads_enabled || con->kthread)
+		return;
+
+	/*
+	 * Printer threads cannot be started as long as any boot console is
+	 * registered because there is no way to synchronize the hardware
+	 * registers between boot console code and regular console code.
+	 */
+	if (have_boot_console)
+		return;
+
+	kt = kthread_run(nbcon_kthread_func, con, "pr/%s%d", con->name, con->index);
+	if (IS_ERR(kt)) {
+		con_printk(KERN_ERR, con, "failed to start printing thread\n");
+		return;
+	}
+
+	con->kthread = kt;
+
+	/*
+	 * It is important that console printing threads are scheduled
+	 * shortly after a printk call and with generous runtime budgets.
+	 */
+	sched_set_normal(con->kthread, -20);
+}
+
+static int __init printk_setup_threads(void)
+{
+	struct console *con;
+
+	console_list_lock();
+	printk_threads_enabled = true;
+	for_each_console(con)
+		nbcon_kthread_create(con);
+	if (IS_ENABLED(CONFIG_PREEMPT_RT) && printing_via_unlock)
+		nbcon_legacy_kthread_create();
+	console_list_unlock();
+	return 0;
+}
+early_initcall(printk_setup_threads);
+
 /**
  * nbcon_alloc - Allocate buffers needed by the nbcon console
  * @con:	Console to allocate buffers for
@@ -1007,8 +1556,11 @@ void nbcon_init(struct console *con)
 	/* nbcon_alloc() must have been called and successful! */
 	BUG_ON(!con->pbufs);
 
+	rcuwait_init(&con->rcuwait);
+	init_irq_work(&con->irq_work, nbcon_irq_work);
 	nbcon_seq_force(con, con->seq);
 	nbcon_state_set(con, &state);
+	nbcon_kthread_create(con);
 }
 
 /**
@@ -1019,6 +1571,7 @@ void nbcon_free(struct console *con)
 {
 	struct nbcon_state state = { };
 
+	nbcon_kthread_stop(con);
 	nbcon_state_set(con, &state);
 
 	/* Boot consoles share global printk buffers. */
@@ -1027,3 +1580,117 @@ void nbcon_free(struct console *con)
 
 	con->pbufs = NULL;
 }
+
+static inline bool uart_is_nbcon(struct uart_port *up)
+{
+	int cookie;
+	bool ret;
+
+	if (!uart_console(up))
+		return false;
+
+	cookie = console_srcu_read_lock();
+	ret = (console_srcu_read_flags(up->cons) & CON_NBCON);
+	console_srcu_read_unlock(cookie);
+	return ret;
+}
+
+/**
+ * nbcon_handle_port_lock - The second half of the port locking wrapper
+ * @up:		The uart port whose @lock was locked
+ *
+ * The uart_port_lock() wrappers will first lock the spin_lock @up->lock.
+ * Then this function is called to implement nbcon-specific processing.
+ *
+ * If @up is an nbcon console, this console will be acquired and marked as
+ * unsafe. Otherwise this function does nothing.
+ *
+ * nbcon consoles acquired via the port lock wrapper always use priority
+ * NBCON_PRIO_NORMAL.
+ */
+void nbcon_handle_port_lock(struct uart_port *up)
+{
+	struct console *con = up->cons;
+	struct nbcon_context ctxt;
+
+	if (!uart_is_nbcon(up))
+		return;
+
+	WARN_ON_ONCE(con->locked_port);
+
+	do {
+		do {
+			memset(&ctxt, 0, sizeof(ctxt));
+			ctxt.console	= con;
+			ctxt.prio	= NBCON_PRIO_NORMAL;
+		} while (!nbcon_context_try_acquire(&ctxt));
+
+	} while (!nbcon_context_enter_unsafe(&ctxt));
+
+	con->locked_port = true;
+}
+EXPORT_SYMBOL_GPL(nbcon_handle_port_lock);
+
+/**
+ * nbcon_handle_port_unlock - The first half of the port unlocking wrapper
+ * @up:		The uart port whose @lock is about to be unlocked
+ *
+ * The uart_port_unlock() wrappers will first call this function to implement
+ * nbcon-specific processing. Then afterwards the uart_port_unlock() wrappers
+ * will unlock the spin_lock @up->lock.
+ *
+ * If @up is an nbcon console, the console will be marked as safe and
+ * released. Otherwise this function does nothing.
+ *
+ * nbcon consoles acquired via the port lock wrapper always use priority
+ * NBCON_PRIO_NORMAL.
+ */
+void nbcon_handle_port_unlock(struct uart_port *up)
+{
+	struct console *con = up->cons;
+	struct nbcon_context ctxt = {
+		.console	= con,
+		.prio		= NBCON_PRIO_NORMAL,
+	};
+
+	if (!uart_is_nbcon(up))
+		return;
+
+	WARN_ON_ONCE(!con->locked_port);
+
+	if (nbcon_context_exit_unsafe(&ctxt))
+		nbcon_context_release(&ctxt);
+
+	con->locked_port = false;
+}
+EXPORT_SYMBOL_GPL(nbcon_handle_port_unlock);
+
+/**
+ * printk_kthread_shutdown - shutdown all threaded printers
+ *
+ * On system shutdown all threaded printers are stopped. This allows printk
+ * to transition back to atomic printing, thus providing a robust mechanism
+ * for the final shutdown/reboot messages to be output.
+ */
+static void printk_kthread_shutdown(void)
+{
+	struct console *con;
+
+	console_list_lock();
+	for_each_console(con) {
+		if (con->flags & CON_NBCON)
+			nbcon_kthread_stop(con);
+	}
+	console_list_unlock();
+}
+
+static struct syscore_ops printk_syscore_ops = {
+	.shutdown = printk_kthread_shutdown,
+};
+
+static int __init printk_init_ops(void)
+{
+	register_syscore_ops(&printk_syscore_ops);
+	return 0;
+}
+device_initcall(printk_init_ops);
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index f2444b581e16c..ff02cb20ac35f 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -282,6 +282,7 @@ EXPORT_SYMBOL(console_list_unlock);
  * Return: A cookie to pass to console_srcu_read_unlock().
  */
 int console_srcu_read_lock(void)
+	__acquires(&console_srcu)
 {
 	return srcu_read_lock_nmisafe(&console_srcu);
 }
@@ -295,6 +296,7 @@ EXPORT_SYMBOL(console_srcu_read_lock);
  * Counterpart to console_srcu_read_lock()
  */
 void console_srcu_read_unlock(int cookie)
+	__releases(&console_srcu)
 {
 	srcu_read_unlock_nmisafe(&console_srcu, cookie);
 }
@@ -347,6 +349,29 @@ static bool panic_in_progress(void)
 	return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID);
 }
 
+/* Return true if a panic is in progress on the current CPU. */
+bool this_cpu_in_panic(void)
+{
+	/*
+	 * We can use raw_smp_processor_id() here because it is impossible for
+	 * the task to be migrated to the panic_cpu, or away from it. If
+	 * panic_cpu has already been set, and we're not currently executing on
+	 * that CPU, then we never will be.
+	 */
+	return unlikely(atomic_read(&panic_cpu) == raw_smp_processor_id());
+}
+
+/*
+ * Return true if a panic is in progress on a remote CPU.
+ *
+ * On true, the local CPU should immediately release any printing resources
+ * that may be needed by the panic CPU.
+ */
+bool other_cpu_in_panic(void)
+{
+	return (panic_in_progress() && !this_cpu_in_panic());
+}
+
 /*
  * This is used for debugging the mess that is the VT code by
  * keeping track if we have the console semaphore held. It's
@@ -438,6 +463,21 @@ static int console_msg_format = MSG_FORMAT_DEFAULT;
 /* syslog_lock protects syslog_* variables and write access to clear_seq. */
 static DEFINE_MUTEX(syslog_lock);
 
+/*
+ * Specifies if a legacy console is registered. If legacy consoles are
+ * present, it is necessary to perform the console_lock/console_unlock dance
+ * whenever console flushing should occur.
+ */
+bool have_legacy_console;
+
+/*
+ * Specifies if a boot console is registered. If boot consoles are present,
+ * nbcon consoles cannot print simultaneously and must be synchronized by
+ * the console lock. This is because boot consoles and nbcon consoles may
+ * have mapped the same hardware.
+ */
+bool have_boot_console;
+
 #ifdef CONFIG_PRINTK
 /*
  * During panic, heavy printk by other CPUs can delay the
@@ -446,6 +486,9 @@ static DEFINE_MUTEX(syslog_lock);
 static int __read_mostly suppress_panic_printk;
 
 DECLARE_WAIT_QUEUE_HEAD(log_wait);
+
+static DECLARE_WAIT_QUEUE_HEAD(legacy_wait);
+
 /* All 3 protected by @syslog_lock. */
 /* the next printk record to read by syslog(READ) or /proc/kmsg */
 static u64 syslog_seq;
@@ -1846,10 +1889,23 @@ static bool console_waiter;
  */
 static void console_lock_spinning_enable(void)
 {
+	/*
+	 * Do not use spinning in panic(). The panic CPU wants to keep the lock.
+	 * Non-panic CPUs abandon the flush anyway.
+	 *
+	 * Just keep the lockdep annotation. The panic-CPU should avoid
+	 * taking console_owner_lock because it might cause a deadlock.
+	 * This looks like the easiest way how to prevent false lockdep
+	 * reports without handling races a lockless way.
+	 */
+	if (panic_in_progress())
+		goto lockdep;
+
 	raw_spin_lock(&console_owner_lock);
 	console_owner = current;
 	raw_spin_unlock(&console_owner_lock);
 
+lockdep:
 	/* The waiter may spin on us after setting console_owner */
 	spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
 }
@@ -1874,6 +1930,22 @@ static int console_lock_spinning_disable_and_check(int cookie)
 {
 	int waiter;
 
+	/*
+	 * Ignore spinning waiters during panic() because they might get stopped
+	 * or blocked at any time,
+	 *
+	 * It is safe because nobody is allowed to start spinning during panic
+	 * in the first place. If there has been a waiter then non panic CPUs
+	 * might stay spinning. They would get stopped anyway. The panic context
+	 * will never start spinning and an interrupted spin on panic CPU will
+	 * never continue.
+	 */
+	if (panic_in_progress()) {
+		/* Keep lockdep happy. */
+		spin_release(&console_owner_dep_map, _THIS_IP_);
+		return 0;
+	}
+
 	raw_spin_lock(&console_owner_lock);
 	waiter = READ_ONCE(console_waiter);
 	console_owner = NULL;
@@ -2263,28 +2335,71 @@ asmlinkage int vprintk_emit(int facility, int level,
 			    const struct dev_printk_info *dev_info,
 			    const char *fmt, va_list args)
 {
+	static atomic_t panic_noise_count = ATOMIC_INIT(0);
+
+	bool do_trylock_unlock = printing_via_unlock && !IS_ENABLED(CONFIG_PREEMPT_RT);
 	int printed_len;
-	bool in_sched = false;
 
 	/* Suppress unimportant messages after panic happens */
 	if (unlikely(suppress_printk))
 		return 0;
 
-	if (unlikely(suppress_panic_printk) &&
-	    atomic_read(&panic_cpu) != raw_smp_processor_id())
-		return 0;
+	if (other_cpu_in_panic()) {
+		if (unlikely(suppress_panic_printk))
+			return 0;
+
+		/*
+		 * The messages on the panic CPU are the most important. If
+		 * non-panic CPUs are generating many messages, the panic
+		 * messages could get lost. Limit the number of non-panic
+		 * messages to approximately 1/4 of the ringbuffer.
+		 */
+		if (atomic_inc_return_relaxed(&panic_noise_count) >
+		    (1 << (prb->desc_ring.count_bits - 2))) {
+			suppress_panic_printk = 1;
+			return 0;
+		}
+	}
 
 	if (level == LOGLEVEL_SCHED) {
 		level = LOGLEVEL_DEFAULT;
-		in_sched = true;
+		/* If called from the scheduler, we can not call up(). */
+		do_trylock_unlock = false;
 	}
 
 	printk_delay(level);
 
 	printed_len = vprintk_store(facility, level, dev_info, fmt, args);
 
-	/* If called from the scheduler, we can not call up(). */
-	if (!in_sched) {
+	/*
+	 * There are 3 situations where nbcon atomic printing should happen in
+	 * the printk() caller context:
+	 *
+	 * 1. When booting, before the printing threads have been started.
+	 *
+	 * 2. During shutdown, since the printing threads may not get a
+	 *    chance to print the final messages.
+	 *
+	 * 3. When this CPU is in panic.
+	 *
+	 * Note that if boot consoles are registered (have_boot_console), the
+	 * console_lock/console_unlock dance must be relied upon instead
+	 * because nbcon consoles cannot print simultaneously with boot
+	 * consoles.
+	 */
+	if (!have_boot_console) {
+		if (!printk_threads_enabled ||
+		    (system_state > SYSTEM_RUNNING) ||
+		    this_cpu_in_panic()) {
+			preempt_disable();
+			nbcon_atomic_flush_all();
+			preempt_enable();
+		}
+	}
+
+	nbcon_wake_threads();
+
+	if (do_trylock_unlock) {
 		/*
 		 * The caller may be holding system-critical or
 		 * timing-sensitive locks. Disable preemption during
@@ -2293,21 +2408,23 @@ asmlinkage int vprintk_emit(int facility, int level,
 		 * another printk() caller will take over the printing.
 		 */
 		preempt_disable();
-		/*
-		 * Try to acquire and then immediately release the console
-		 * semaphore. The release will print out buffers. With the
-		 * spinning variant, this context tries to take over the
-		 * printing from another printing context.
-		 */
-		if (console_trylock_spinning())
-			console_unlock();
+		if (nbcon_get_default_prio() != NBCON_PRIO_EMERGENCY) {
+			/*
+			 * Try to acquire and then immediately release the
+			 * console semaphore. The release will print out
+			 * buffers. With the spinning variant, this context
+			 * tries to take over the printing from another
+			 * printing context.
+			 */
+			if (console_trylock_spinning())
+				console_unlock();
+		}
 		preempt_enable();
-	}
 
-	if (in_sched)
-		defer_console_output();
-	else
 		wake_up_klogd();
+	} else {
+		defer_console_output();
+	}
 
 	return printed_len;
 }
@@ -2335,6 +2452,14 @@ EXPORT_SYMBOL(_printk);
 static bool pr_flush(int timeout_ms, bool reset_on_progress);
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
 
+static struct task_struct *nbcon_legacy_kthread;
+
+static inline void wake_up_legacy_kthread(void)
+{
+	if (nbcon_legacy_kthread)
+		wake_up_interruptible(&legacy_wait);
+}
+
 #else /* CONFIG_PRINTK */
 
 #define printk_time		false
@@ -2347,7 +2472,8 @@ static u64 syslog_seq;
 
 static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true; }
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
-
+static inline void nbcon_legacy_kthread_create(void) { }
+static inline void wake_up_legacy_kthread(void) { }
 #endif /* CONFIG_PRINTK */
 
 #ifdef CONFIG_EARLY_PRINTK
@@ -2563,6 +2689,8 @@ void suspend_console(void)
 void resume_console(void)
 {
 	struct console *con;
+	short flags;
+	int cookie;
 
 	if (!console_suspend_enabled)
 		return;
@@ -2579,6 +2707,21 @@ void resume_console(void)
 	 */
 	synchronize_srcu(&console_srcu);
 
+	/*
+	 * Since this runs in task context, wake the threaded printers
+	 * directly rather than scheduling irq_work to do it.
+	 */
+
+	cookie = console_srcu_read_lock();
+	for_each_console_srcu(con) {
+		flags = console_srcu_read_flags(con);
+		if (flags & CON_NBCON)
+			nbcon_kthread_wake(con);
+	}
+	console_srcu_read_unlock(cookie);
+
+	wake_up_legacy_kthread();
+
 	pr_flush(1000, true);
 }
 
@@ -2593,7 +2736,8 @@ void resume_console(void)
  */
 static int console_cpu_notify(unsigned int cpu)
 {
-	if (!cpuhp_tasks_frozen) {
+	if (!cpuhp_tasks_frozen && printing_via_unlock &&
+	    !IS_ENABLED(CONFIG_PREEMPT_RT)) {
 		/* If trylock fails, someone else is doing the printing */
 		if (console_trylock())
 			console_unlock();
@@ -2601,26 +2745,6 @@ static int console_cpu_notify(unsigned int cpu)
 	return 0;
 }
 
-/*
- * Return true if a panic is in progress on a remote CPU.
- *
- * On true, the local CPU should immediately release any printing resources
- * that may be needed by the panic CPU.
- */
-bool other_cpu_in_panic(void)
-{
-	if (!panic_in_progress())
-		return false;
-
-	/*
-	 * We can use raw_smp_processor_id() here because it is impossible for
-	 * the task to be migrated to the panic_cpu, or away from it. If
-	 * panic_cpu has already been set, and we're not currently executing on
-	 * that CPU, then we never will be.
-	 */
-	return atomic_read(&panic_cpu) != raw_smp_processor_id();
-}
-
 /**
  * console_lock - block the console subsystem from printing
  *
@@ -2670,36 +2794,6 @@ int is_console_locked(void)
 }
 EXPORT_SYMBOL(is_console_locked);
 
-/*
- * Check if the given console is currently capable and allowed to print
- * records.
- *
- * Requires the console_srcu_read_lock.
- */
-static inline bool console_is_usable(struct console *con)
-{
-	short flags = console_srcu_read_flags(con);
-
-	if (!(flags & CON_ENABLED))
-		return false;
-
-	if ((flags & CON_SUSPENDED))
-		return false;
-
-	if (!con->write)
-		return false;
-
-	/*
-	 * Console drivers may assume that per-cpu resources have been
-	 * allocated. So unless they're explicitly marked as being able to
-	 * cope (CON_ANYTIME) don't call them until this CPU is officially up.
-	 */
-	if (!cpu_online(raw_smp_processor_id()) && !(flags & CON_ANYTIME))
-		return false;
-
-	return true;
-}
-
 static void __console_unlock(void)
 {
 	console_locked = 0;
@@ -2776,8 +2870,6 @@ void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
 bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
 			     bool is_extended, bool may_suppress)
 {
-	static int panic_console_dropped;
-
 	struct printk_buffers *pbufs = pmsg->pbufs;
 	const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
 	const size_t outbuf_sz = sizeof(pbufs->outbuf);
@@ -2805,17 +2897,6 @@ bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
 	pmsg->seq = r.info->seq;
 	pmsg->dropped = r.info->seq - seq;
 
-	/*
-	 * Check for dropped messages in panic here so that printk
-	 * suppression can occur as early as possible if necessary.
-	 */
-	if (pmsg->dropped &&
-	    panic_in_progress() &&
-	    panic_console_dropped++ > 10) {
-		suppress_panic_printk = 1;
-		pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n");
-	}
-
 	/* Skip record that has level above the console loglevel. */
 	if (may_suppress && suppress_message_printing(r.info->level))
 		goto out;
@@ -2881,31 +2962,38 @@ static bool console_emit_next_record(struct console *con, bool *handover, int co
 		con->dropped = 0;
 	}
 
-	/*
-	 * While actively printing out messages, if another printk()
-	 * were to occur on another CPU, it may wait for this one to
-	 * finish. This task can not be preempted if there is a
-	 * waiter waiting to take over.
-	 *
-	 * Interrupts are disabled because the hand over to a waiter
-	 * must not be interrupted until the hand over is completed
-	 * (@console_waiter is cleared).
-	 */
-	printk_safe_enter_irqsave(flags);
-	console_lock_spinning_enable();
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		/*
+		 * While actively printing out messages, if another printk()
+		 * were to occur on another CPU, it may wait for this one to
+		 * finish. This task can not be preempted if there is a
+		 * waiter waiting to take over.
+		 *
+		 * Interrupts are disabled because the hand over to a waiter
+		 * must not be interrupted until the hand over is completed
+		 * (@console_waiter is cleared).
+		 */
+		printk_safe_enter_irqsave(flags);
+		console_lock_spinning_enable();
 
-	/* Do not trace print latency. */
-	stop_critical_timings();
+		/* Do not trace print latency. */
+		stop_critical_timings();
+	}
 
 	/* Write everything out to the hardware. */
 	con->write(con, outbuf, pmsg.outbuf_len);
 
-	start_critical_timings();
-
 	con->seq = pmsg.seq + 1;
 
-	*handover = console_lock_spinning_disable_and_check(cookie);
-	printk_safe_exit_irqrestore(flags);
+	if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		*handover = false;
+	} else {
+		start_critical_timings();
+
+		*handover = console_lock_spinning_disable_and_check(cookie);
+
+		printk_safe_exit_irqrestore(flags);
+	}
 skip:
 	return true;
 }
@@ -2958,24 +3046,40 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
 
 		cookie = console_srcu_read_lock();
 		for_each_console_srcu(con) {
+			short flags = console_srcu_read_flags(con);
+			u64 printk_seq;
 			bool progress;
 
-			if (!console_is_usable(con))
+			/*
+			 * console_flush_all() is only for legacy consoles,
+			 * unless the nbcon console has no kthread printer.
+			 */
+			if ((flags & CON_NBCON) && con->kthread)
+				continue;
+
+			if (!console_is_usable(con, flags, true))
 				continue;
 			any_usable = true;
 
-			progress = console_emit_next_record(con, handover, cookie);
+			if (flags & CON_NBCON) {
+				progress = nbcon_atomic_emit_next_record(con);
+				printk_seq = nbcon_seq_read(con);
+			} else {
+				progress = console_emit_next_record(con, handover, cookie);
 
-			/*
-			 * If a handover has occurred, the SRCU read lock
-			 * is already released.
-			 */
-			if (*handover)
-				return false;
+				/*
+				 * If a handover has occurred, the SRCU read
+				 * lock is already released.
+				 */
+				if (*handover)
+					return false;
+
+				printk_seq = con->seq;
+			}
 
 			/* Track the next of the highest seq flushed. */
-			if (con->seq > *next_seq)
-				*next_seq = con->seq;
+			if (printk_seq > *next_seq)
+				*next_seq = printk_seq;
 
 			if (!progress)
 				continue;
@@ -2998,19 +3102,7 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
 	return false;
 }
 
-/**
- * console_unlock - unblock the console subsystem from printing
- *
- * Releases the console_lock which the caller holds to block printing of
- * the console subsystem.
- *
- * While the console_lock was held, console output may have been buffered
- * by printk().  If this is the case, console_unlock(); emits
- * the output prior to releasing the lock.
- *
- * console_unlock(); may be called from any context.
- */
-void console_unlock(void)
+static u64 console_flush_and_unlock(void)
 {
 	bool do_cond_resched;
 	bool handover;
@@ -3053,6 +3145,34 @@ void console_unlock(void)
 		 * fails, another context is already handling the printing.
 		 */
 	} while (prb_read_valid(prb, next_seq, NULL) && console_trylock());
+
+	return next_seq;
+}
+
+/**
+ * console_unlock - unblock the console subsystem from printing
+ *
+ * Releases the console_lock which the caller holds to block printing of
+ * the console subsystem.
+ *
+ * While the console_lock was held, console output may have been buffered
+ * by printk().  If this is the case, console_unlock(); emits
+ * the output prior to releasing the lock.
+ *
+ * console_unlock(); may be called from any context.
+ */
+void console_unlock(void)
+{
+	/*
+	 * PREEMPT_RT relies on kthread and atomic consoles for printing.
+	 * It never attempts to print from console_unlock().
+	 */
+	if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		__console_unlock();
+		return;
+	}
+
+	console_flush_and_unlock();
 }
 EXPORT_SYMBOL(console_unlock);
 
@@ -3187,7 +3307,11 @@ void console_flush_on_panic(enum con_flush_mode mode)
 		console_srcu_read_unlock(cookie);
 	}
 
-	console_flush_all(false, &next_seq, &handover);
+	if (!have_boot_console)
+		nbcon_atomic_flush_all();
+
+	if (printing_via_unlock)
+		console_flush_all(false, &next_seq, &handover);
 }
 
 /*
@@ -3244,13 +3368,122 @@ EXPORT_SYMBOL(console_stop);
 
 void console_start(struct console *console)
 {
+	short flags;
+
 	console_list_lock();
 	console_srcu_write_flags(console, console->flags | CON_ENABLED);
+	flags = console->flags;
 	console_list_unlock();
+
+	/*
+	 * Ensure that all SRCU list walks have completed. The related
+	 * printing context must be able to see it is enabled so that
+	 * it is guaranteed to wake up and resume printing.
+	 */
+	synchronize_srcu(&console_srcu);
+
+	if (flags & CON_NBCON)
+		nbcon_kthread_wake(console);
+	else
+		wake_up_legacy_kthread();
+
 	__pr_flush(console, 1000, true);
 }
 EXPORT_SYMBOL(console_start);
 
+#ifdef CONFIG_PRINTK
+static bool printer_should_wake(u64 seq)
+{
+	bool available = false;
+	struct console *con;
+	int cookie;
+
+	if (kthread_should_stop())
+		return true;
+
+	cookie = console_srcu_read_lock();
+	for_each_console_srcu(con) {
+		short flags = console_srcu_read_flags(con);
+		u64 printk_seq;
+
+		/*
+		 * The legacy printer thread is only for legacy consoles,
+		 * unless the nbcon console has no kthread printer.
+		 */
+		if ((flags & CON_NBCON) && con->kthread)
+			continue;
+
+		if (!console_is_usable(con, flags, true))
+			continue;
+
+		if (flags & CON_NBCON) {
+			printk_seq = nbcon_seq_read(con);
+		} else {
+			/*
+			 * It is safe to read @seq because only this
+			 * thread context updates @seq.
+			 */
+			printk_seq = con->seq;
+		}
+
+		if (prb_read_valid(prb, printk_seq, NULL)) {
+			available = true;
+			break;
+		}
+	}
+	console_srcu_read_unlock(cookie);
+
+	return available;
+}
+
+static int nbcon_legacy_kthread_func(void *unused)
+{
+	u64 seq = 0;
+	int error;
+
+	for (;;) {
+		error = wait_event_interruptible(legacy_wait, printer_should_wake(seq));
+
+		if (kthread_should_stop())
+			break;
+
+		if (error)
+			continue;
+
+		console_lock();
+		seq = console_flush_and_unlock();
+	}
+	return 0;
+}
+
+void nbcon_legacy_kthread_create(void)
+{
+	struct task_struct *kt;
+
+	lockdep_assert_held(&console_mutex);
+
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		return;
+
+	if (!printk_threads_enabled || nbcon_legacy_kthread)
+		return;
+
+	kt = kthread_run(nbcon_legacy_kthread_func, NULL, "pr/legacy");
+	if (IS_ERR(kt)) {
+		pr_err("unable to start legacy printing thread\n");
+		return;
+	}
+
+	nbcon_legacy_kthread = kt;
+
+	/*
+	 * It is important that console printing threads are scheduled
+	 * shortly after a printk call and with generous runtime budgets.
+	 */
+	sched_set_normal(nbcon_legacy_kthread, -20);
+}
+#endif /* CONFIG_PRINTK */
+
 static int __read_mostly keep_bootcon;
 
 static int __init keep_bootcon_setup(char *str)
@@ -3503,8 +3736,15 @@ void register_console(struct console *newcon)
 	newcon->dropped = 0;
 	console_init_seq(newcon, bootcon_registered);
 
-	if (newcon->flags & CON_NBCON)
+	if (newcon->flags & CON_NBCON) {
 		nbcon_init(newcon);
+	} else {
+		have_legacy_console = true;
+		nbcon_legacy_kthread_create();
+	}
+
+	if (newcon->flags & CON_BOOT)
+		have_boot_console = true;
 
 	/*
 	 * Put this console in the list - keep the
@@ -3558,6 +3798,9 @@ EXPORT_SYMBOL(register_console);
 /* Must be called under console_list_lock(). */
 static int unregister_console_locked(struct console *console)
 {
+	bool is_legacy_con = !(console->flags & CON_NBCON);
+	bool is_boot_con = (console->flags & CON_BOOT);
+	struct console *c;
 	int res;
 
 	lockdep_assert_console_list_lock_held();
@@ -3605,6 +3848,42 @@ static int unregister_console_locked(struct console *console)
 	if (console->exit)
 		res = console->exit(console);
 
+	/*
+	 * If this console was a boot and/or legacy console, the
+	 * related global flags might need to be updated.
+	 */
+	if (is_boot_con || is_legacy_con) {
+		bool found_legacy_con = false;
+		bool found_boot_con = false;
+
+		for_each_console(c) {
+			if (c->flags & CON_BOOT)
+				found_boot_con = true;
+			if (!(c->flags & CON_NBCON))
+				found_legacy_con = true;
+		}
+		if (!found_boot_con)
+			have_boot_console = false;
+		if (!found_legacy_con)
+			have_legacy_console = false;
+	}
+
+	/*
+	 * When the last boot console unregisters, start up the
+	 * printing threads.
+	 */
+	if (is_boot_con && !have_boot_console) {
+		for_each_console(c)
+			nbcon_kthread_create(c);
+	}
+
+#ifdef CONFIG_PRINTK
+	if (!printing_via_unlock && nbcon_legacy_kthread) {
+		kthread_stop(nbcon_legacy_kthread);
+		nbcon_legacy_kthread = NULL;
+	}
+#endif
+
 	return res;
 }
 
@@ -3755,31 +4034,42 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
 	u64 last_diff = 0;
 	u64 printk_seq;
 	short flags;
+	bool locked;
 	int cookie;
 	u64 diff;
 	u64 seq;
 
 	might_sleep();
 
-	seq = prb_next_seq(prb);
+	seq = prb_next_reserve_seq(prb);
 
-	/* Flush the consoles so that records up to @seq are printed. */
-	console_lock();
-	console_unlock();
+	/*
+	 * Flush the consoles so that records up to @seq are printed.
+	 * Otherwise this function will just wait for the threaded printers
+	 * to print up to @seq.
+	 */
+	if (printing_via_unlock && !IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		console_lock();
+		console_unlock();
+	}
 
 	for (;;) {
 		unsigned long begin_jiffies;
 		unsigned long slept_jiffies;
 
+		locked = false;
 		diff = 0;
 
-		/*
-		 * Hold the console_lock to guarantee safe access to
-		 * console->seq. Releasing console_lock flushes more
-		 * records in case @seq is still not printed on all
-		 * usable consoles.
-		 */
-		console_lock();
+		if (printing_via_unlock) {
+			/*
+			 * Hold the console_lock to guarantee safe access to
+			 * console->seq. Releasing console_lock flushes more
+			 * records in case @seq is still not printed on all
+			 * usable consoles.
+			 */
+			console_lock();
+			locked = true;
+		}
 
 		cookie = console_srcu_read_lock();
 		for_each_console_srcu(c) {
@@ -3793,12 +4083,15 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
 			 * that they make forward progress, so only increment
 			 * @diff for usable consoles.
 			 */
-			if (!console_is_usable(c))
+			if (!console_is_usable(c, flags, true) &&
+			    !console_is_usable(c, flags, false)) {
 				continue;
+			}
 
 			if (flags & CON_NBCON) {
 				printk_seq = nbcon_seq_read(c);
 			} else {
+				WARN_ON_ONCE(!locked);
 				printk_seq = c->seq;
 			}
 
@@ -3810,7 +4103,8 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
 		if (diff != last_diff && reset_on_progress)
 			remaining_jiffies = timeout_jiffies;
 
-		console_unlock();
+		if (locked)
+			console_unlock();
 
 		/* Note: @diff is 0 if there are no usable consoles. */
 		if (diff == 0 || remaining_jiffies == 0)
@@ -3862,9 +4156,16 @@ static void wake_up_klogd_work_func(struct irq_work *irq_work)
 	int pending = this_cpu_xchg(printk_pending, 0);
 
 	if (pending & PRINTK_PENDING_OUTPUT) {
-		/* If trylock fails, someone else is doing the printing */
-		if (console_trylock())
-			console_unlock();
+		if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+			wake_up_interruptible(&legacy_wait);
+		} else {
+			/*
+			 * If trylock fails, some other context
+			 * will do the printing.
+			 */
+			if (console_trylock())
+				console_unlock();
+		}
 	}
 
 	if (pending & PRINTK_PENDING_WAKEUP)
@@ -3932,11 +4233,30 @@ void defer_console_output(void)
 	 * New messages may have been added directly to the ringbuffer
 	 * using vprintk_store(), so wake any waiters as well.
 	 */
-	__wake_up_klogd(PRINTK_PENDING_WAKEUP | PRINTK_PENDING_OUTPUT);
+	int val = PRINTK_PENDING_WAKEUP;
+
+	if (printing_via_unlock)
+		val |= PRINTK_PENDING_OUTPUT;
+	__wake_up_klogd(val);
 }
 
+/**
+ * printk_trigger_flush() - Make sure that the consoles will get flushed
+ *
+ * Try to flush consoles when possible or queue flushing consoles like
+ * in the deferred printk.
+ *
+ * Context: Can be used in any context
+ */
 void printk_trigger_flush(void)
 {
+	if (!have_boot_console) {
+		preempt_disable();
+		nbcon_atomic_flush_all();
+		preempt_enable();
+	}
+
+	nbcon_wake_threads();
 	defer_console_output();
 }
 
diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
index fde338606ce83..2b2a85222d19d 100644
--- a/kernel/printk/printk_ringbuffer.c
+++ b/kernel/printk/printk_ringbuffer.c
@@ -6,6 +6,7 @@
 #include <linux/errno.h>
 #include <linux/bug.h>
 #include "printk_ringbuffer.h"
+#include "internal.h"
 
 /**
  * DOC: printk_ringbuffer overview
@@ -303,6 +304,9 @@
  *
  *   desc_push_tail:B / desc_reserve:D
  *     set descriptor reusable (state), then push descriptor tail (id)
+ *
+ *   desc_update_last_finalized:A / desc_last_finalized_seq:A
+ *     store finalized record, then set new highest finalized sequence number
  */
 
 #define DATA_SIZE(data_ring)		_DATA_SIZE((data_ring)->size_bits)
@@ -1030,9 +1034,13 @@ static char *data_alloc(struct printk_ringbuffer *rb, unsigned int size,
 	unsigned long next_lpos;
 
 	if (size == 0) {
-		/* Specify a data-less block. */
-		blk_lpos->begin = NO_LPOS;
-		blk_lpos->next = NO_LPOS;
+		/*
+		 * Data blocks are not created for empty lines. Instead, the
+		 * reader will recognize these special lpos values and handle
+		 * it appropriately.
+		 */
+		blk_lpos->begin = EMPTY_LINE_LPOS;
+		blk_lpos->next = EMPTY_LINE_LPOS;
 		return NULL;
 	}
 
@@ -1210,10 +1218,18 @@ static const char *get_data(struct prb_data_ring *data_ring,
 
 	/* Data-less data block description. */
 	if (BLK_DATALESS(blk_lpos)) {
-		if (blk_lpos->begin == NO_LPOS && blk_lpos->next == NO_LPOS) {
+		/*
+		 * Records that are just empty lines are also valid, even
+		 * though they do not have a data block. For such records
+		 * explicitly return empty string data to signify success.
+		 */
+		if (blk_lpos->begin == EMPTY_LINE_LPOS &&
+		    blk_lpos->next == EMPTY_LINE_LPOS) {
 			*data_size = 0;
 			return "";
 		}
+
+		/* Data lost, invalid, or otherwise unavailable. */
 		return NULL;
 	}
 
@@ -1441,20 +1457,144 @@ bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer
 	return false;
 }
 
+#ifdef CONFIG_64BIT
+
+#define __u64seq_to_ulseq(u64seq) (u64seq)
+#define __ulseq_to_u64seq(ulseq) (ulseq)
+
+#else /* CONFIG_64BIT */
+
+static u64 prb_first_seq(struct printk_ringbuffer *rb);
+
+#define __u64seq_to_ulseq(u64seq) ((u32)u64seq)
+static inline u64 __ulseq_to_u64seq(u32 ulseq)
+{
+	u64 rb_first_seq = prb_first_seq(prb);
+	u64 seq;
+
+	/*
+	 * The provided sequence is only the lower 32 bits of the ringbuffer
+	 * sequence. It needs to be expanded to 64bit. Get the first sequence
+	 * number from the ringbuffer and fold it.
+	 */
+	seq = rb_first_seq - ((s32)((u32)rb_first_seq - ulseq));
+
+	return seq;
+}
+
+#endif /* CONFIG_64BIT */
+
+/*
+ * @last_finalized_seq value guarantees that all records up to and including
+ * this sequence number are finalized and can be read. The only exception are
+ * too old records which have already been overwritten.
+ *
+ * It is also guaranteed that @last_finalized_seq only increases.
+ *
+ * Be aware that finalized records following non-finalized records are not
+ * reported because they are not yet available to the reader. For example,
+ * a new record stored via printk() will not be available to a printer if
+ * it follows a record that has not been finalized yet. However, once that
+ * non-finalized record becomes finalized, @last_finalized_seq will be
+ * appropriately updated and the full set of finalized records will be
+ * available to the printer. And since each printk() caller will either
+ * directly print or trigger deferred printing of all available unprinted
+ * records, all printk() messages will get printed.
+ */
+static u64 desc_last_finalized_seq(struct prb_desc_ring *desc_ring)
+{
+	unsigned long ulseq;
+
+	/*
+	 * Guarantee the sequence number is loaded before loading the
+	 * associated record in order to guarantee that the record can be
+	 * seen by this CPU. This pairs with desc_update_last_finalized:A.
+	 */
+	ulseq = atomic_long_read_acquire(&desc_ring->last_finalized_seq
+					); /* LMM(desc_last_finalized_seq:A) */
+
+	return __ulseq_to_u64seq(ulseq);
+}
+
+static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
+			    struct printk_record *r, unsigned int *line_count);
+
+/*
+ * Check if there are records directly following @last_finalized_seq that are
+ * finalized. If so, update @last_finalized_seq to the latest of these
+ * records. It is not allowed to skip over records that are not yet finalized.
+ */
+static void desc_update_last_finalized(struct printk_ringbuffer *rb)
+{
+	struct prb_desc_ring *desc_ring = &rb->desc_ring;
+	u64 old_seq = desc_last_finalized_seq(desc_ring);
+	unsigned long oldval;
+	unsigned long newval;
+	u64 finalized_seq;
+	u64 try_seq;
+
+try_again:
+	finalized_seq = old_seq;
+	try_seq = finalized_seq + 1;
+
+	/* Try to find later finalized records. */
+	while (_prb_read_valid(rb, &try_seq, NULL, NULL)) {
+		finalized_seq = try_seq;
+		try_seq++;
+	}
+
+	/* No update needed if no later finalized record was found. */
+	if (finalized_seq == old_seq)
+		return;
+
+	oldval = __u64seq_to_ulseq(old_seq);
+	newval = __u64seq_to_ulseq(finalized_seq);
+
+	/*
+	 * Set the sequence number of a later finalized record that has been
+	 * seen.
+	 *
+	 * Guarantee the record data is visible to other CPUs before storing
+	 * its sequence number. This pairs with desc_last_finalized_seq:A.
+	 *
+	 * Memory barrier involvement:
+	 *
+	 * If desc_last_finalized_seq:A reads from
+	 * desc_update_last_finalized:A, then desc_read:A reads from
+	 * _prb_commit:B.
+	 *
+	 * Relies on:
+	 *
+	 * RELEASE from _prb_commit:B to desc_update_last_finalized:A
+	 *    matching
+	 * ACQUIRE from desc_last_finalized_seq:A to desc_read:A
+	 *
+	 * Note: _prb_commit:B and desc_update_last_finalized:A can be
+	 *       different CPUs. However, the desc_update_last_finalized:A
+	 *       CPU (which performs the release) must have previously seen
+	 *       _prb_commit:B.
+	 */
+	if (!atomic_long_try_cmpxchg_release(&desc_ring->last_finalized_seq,
+				&oldval, newval)) { /* LMM(desc_update_last_finalized:A) */
+		old_seq = __ulseq_to_u64seq(oldval);
+		goto try_again;
+	}
+}
+
 /*
  * Attempt to finalize a specified descriptor. If this fails, the descriptor
  * is either already final or it will finalize itself when the writer commits.
  */
-static void desc_make_final(struct prb_desc_ring *desc_ring, unsigned long id)
+static void desc_make_final(struct printk_ringbuffer *rb, unsigned long id)
 {
+	struct prb_desc_ring *desc_ring = &rb->desc_ring;
 	unsigned long prev_state_val = DESC_SV(id, desc_committed);
 	struct prb_desc *d = to_desc(desc_ring, id);
 
-	atomic_long_cmpxchg_relaxed(&d->state_var, prev_state_val,
-			DESC_SV(id, desc_finalized)); /* LMM(desc_make_final:A) */
-
-	/* Best effort to remember the last finalized @id. */
-	atomic_long_set(&desc_ring->last_finalized_id, id);
+	if (atomic_long_try_cmpxchg_relaxed(&d->state_var, &prev_state_val,
+			DESC_SV(id, desc_finalized))) { /* LMM(desc_make_final:A) */
+		desc_update_last_finalized(rb);
+	}
 }
 
 /**
@@ -1550,7 +1690,7 @@ bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,
 	 * readers. (For seq==0 there is no previous descriptor.)
 	 */
 	if (info->seq > 0)
-		desc_make_final(desc_ring, DESC_ID(id - 1));
+		desc_make_final(rb, DESC_ID(id - 1));
 
 	r->text_buf = data_alloc(rb, r->text_buf_size, &d->text_blk_lpos, id);
 	/* If text data allocation fails, a data-less record is committed. */
@@ -1643,7 +1783,7 @@ void prb_commit(struct prb_reserved_entry *e)
 	 */
 	head_id = atomic_long_read(&desc_ring->head_id); /* LMM(prb_commit:A) */
 	if (head_id != e->id)
-		desc_make_final(desc_ring, e->id);
+		desc_make_final(e->rb, e->id);
 }
 
 /**
@@ -1663,12 +1803,9 @@ void prb_commit(struct prb_reserved_entry *e)
  */
 void prb_final_commit(struct prb_reserved_entry *e)
 {
-	struct prb_desc_ring *desc_ring = &e->rb->desc_ring;
-
 	_prb_commit(e, desc_finalized);
 
-	/* Best effort to remember the last finalized @id. */
-	atomic_long_set(&desc_ring->last_finalized_id, e->id);
+	desc_update_last_finalized(e->rb);
 }
 
 /*
@@ -1875,12 +2012,114 @@ static u64 prb_first_seq(struct printk_ringbuffer *rb)
 	return seq;
 }
 
-/*
- * Non-blocking read of a record. Updates @seq to the last finalized record
- * (which may have no data available).
+/**
+ * prb_next_reserve_seq() - Get the sequence number after the most recently
+ *                  reserved record.
  *
- * See the description of prb_read_valid() and prb_read_valid_info()
- * for details.
+ * @rb:  The ringbuffer to get the sequence number from.
+ *
+ * This is the public function available to readers to see what sequence
+ * number will be assigned to the next reserved record.
+ *
+ * Note that depending on the situation, this value can be equal to or
+ * higher than the sequence number returned by prb_next_seq().
+ *
+ * Context: Any context.
+ * Return: The sequence number that will be assigned to the next record
+ *         reserved.
+ */
+u64 prb_next_reserve_seq(struct printk_ringbuffer *rb)
+{
+	struct prb_desc_ring *desc_ring = &rb->desc_ring;
+	unsigned long last_finalized_id;
+	atomic_long_t *state_var;
+	u64 last_finalized_seq;
+	unsigned long head_id;
+	struct prb_desc desc;
+	unsigned long diff;
+	struct prb_desc *d;
+	int err;
+
+	/*
+	 * It may not be possible to read a sequence number for @head_id.
+	 * So the ID of @last_finailzed_seq is used to calculate what the
+	 * sequence number of @head_id will be.
+	 */
+
+try_again:
+	last_finalized_seq = desc_last_finalized_seq(desc_ring);
+
+	/*
+	 * @head_id is loaded after @last_finalized_seq to ensure that it is
+	 * at or beyond @last_finalized_seq.
+	 *
+	 * Memory barrier involvement:
+	 *
+	 * If desc_last_finalized_seq:A reads from
+	 * desc_update_last_finalized:A, then
+	 * prb_next_reserve_seq:A reads from desc_reserve:D.
+	 *
+	 * Relies on:
+	 *
+	 * RELEASE from desc_reserve:D to desc_update_last_finalized:A
+	 *    matching
+	 * ACQUIRE from desc_last_finalized_seq:A to prb_next_reserve_seq:A
+	 *
+	 * Note: desc_reserve:D and desc_update_last_finalized:A can be
+	 *       different CPUs. However, the desc_update_last_finalized:A CPU
+	 *       (which performs the release) must have previously seen
+	 *       desc_read:C, which implies desc_reserve:D can be seen.
+	 */
+	head_id = atomic_long_read(&desc_ring->head_id); /* LMM(prb_next_reserve_seq:A) */
+
+	d = to_desc(desc_ring, last_finalized_seq);
+	state_var = &d->state_var;
+
+	/* Extract the ID, used to specify the descriptor to read. */
+	last_finalized_id = DESC_ID(atomic_long_read(state_var));
+
+	/* Ensure @last_finalized_id is correct. */
+	err = desc_read_finalized_seq(desc_ring, last_finalized_id, last_finalized_seq, &desc);
+
+	if (err == -EINVAL) {
+		if (last_finalized_seq == 0) {
+			/*
+			 * @last_finalized_seq still contains its initial
+			 * value. Probably no record has been finalized yet.
+			 * This means the ringbuffer is not yet full and the
+			 * @head_id value can be used directly (subtracting
+			 * off its initial value).
+			 *
+			 * Because of hack#2 of the bootstrapping phase, the
+			 * @head_id initial value must be handled separately.
+			 */
+			if (head_id == DESC0_ID(desc_ring->count_bits))
+				return 0;
+
+			last_finalized_id = DESC0_ID(desc_ring->count_bits) + 1;
+		} else {
+			/* Record must have been overwritten. Try again. */
+			goto try_again;
+		}
+	}
+
+	diff = head_id - last_finalized_id;
+
+	return (last_finalized_seq + diff + 1);
+}
+
+/*
+ * Non-blocking read of a record.
+ *
+ * On success @seq is updated to the record that was read and (if provided)
+ * @r and @line_count will contain the read/calculated data.
+ *
+ * On failure @seq is updated to a record that is not yet available to the
+ * reader, but it will be the next record available to the reader.
+ *
+ * Note: When the current CPU is in panic, this function will skip over any
+ *       non-existent/non-finalized records in order to allow the panic CPU
+ *       to print any and all records that have been finalized.
  */
 static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
 			    struct printk_record *r, unsigned int *line_count)
@@ -1899,12 +2138,26 @@ static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
 			*seq = tail_seq;
 
 		} else if (err == -ENOENT) {
-			/* Record exists, but no data available. Skip. */
+			/* Record exists, but the data was lost. Skip. */
 			(*seq)++;
 
 		} else {
-			/* Non-existent/non-finalized record. Must stop. */
-			return false;
+			/*
+			 * Non-existent/non-finalized record. Must stop.
+			 *
+			 * For panic situations it cannot be expected that
+			 * non-finalized records will become finalized. But
+			 * there may be other finalized records beyond that
+			 * need to be printed for a panic situation. If this
+			 * is the panic CPU, skip this
+			 * non-existent/non-finalized record unless it is
+			 * at or beyond the head, in which case it is not
+			 * possible to continue.
+			 */
+			if (this_cpu_in_panic() && ((*seq + 1) < prb_next_reserve_seq(rb)))
+				(*seq)++;
+			else
+				return false;
 		}
 	}
 
@@ -1932,7 +2185,7 @@ static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
  * On success, the reader must check r->info.seq to see which record was
  * actually read. This allows the reader to detect dropped records.
  *
- * Failure means @seq refers to a not yet written record.
+ * Failure means @seq refers to a record not yet available to the reader.
  */
 bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq,
 		    struct printk_record *r)
@@ -1962,7 +2215,7 @@ bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq,
  * On success, the reader must check info->seq to see which record meta data
  * was actually read. This allows the reader to detect dropped records.
  *
- * Failure means @seq refers to a not yet written record.
+ * Failure means @seq refers to a record not yet available to the reader.
  */
 bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq,
 			 struct printk_info *info, unsigned int *line_count)
@@ -2008,7 +2261,9 @@ u64 prb_first_valid_seq(struct printk_ringbuffer *rb)
  * newest sequence number available to readers will be.
  *
  * This provides readers a sequence number to jump to if all currently
- * available records should be skipped.
+ * available records should be skipped. It is guaranteed that all records
+ * previous to the returned value have been finalized and are (or were)
+ * available to the reader.
  *
  * Context: Any context.
  * Return: The sequence number of the next newest (not yet available) record
@@ -2017,33 +2272,19 @@ u64 prb_first_valid_seq(struct printk_ringbuffer *rb)
 u64 prb_next_seq(struct printk_ringbuffer *rb)
 {
 	struct prb_desc_ring *desc_ring = &rb->desc_ring;
-	enum desc_state d_state;
-	unsigned long id;
 	u64 seq;
 
-	/* Check if the cached @id still points to a valid @seq. */
-	id = atomic_long_read(&desc_ring->last_finalized_id);
-	d_state = desc_read(desc_ring, id, NULL, &seq, NULL);
+	seq = desc_last_finalized_seq(desc_ring);
 
-	if (d_state == desc_finalized || d_state == desc_reusable) {
-		/*
-		 * Begin searching after the last finalized record.
-		 *
-		 * On 0, the search must begin at 0 because of hack#2
-		 * of the bootstrapping phase it is not known if a
-		 * record at index 0 exists.
-		 */
-		if (seq != 0)
-			seq++;
-	} else {
-		/*
-		 * The information about the last finalized sequence number
-		 * has gone. It should happen only when there is a flood of
-		 * new messages and the ringbuffer is rapidly recycled.
-		 * Give up and start from the beginning.
-		 */
-		seq = 0;
-	}
+	/*
+	 * Begin searching after the last finalized record.
+	 *
+	 * On 0, the search must begin at 0 because of hack#2
+	 * of the bootstrapping phase it is not known if a
+	 * record at index 0 exists.
+	 */
+	if (seq != 0)
+		seq++;
 
 	/*
 	 * The information about the last finalized @seq might be inaccurate.
@@ -2085,7 +2326,7 @@ void prb_init(struct printk_ringbuffer *rb,
 	rb->desc_ring.infos = infos;
 	atomic_long_set(&rb->desc_ring.head_id, DESC0_ID(descbits));
 	atomic_long_set(&rb->desc_ring.tail_id, DESC0_ID(descbits));
-	atomic_long_set(&rb->desc_ring.last_finalized_id, DESC0_ID(descbits));
+	atomic_long_set(&rb->desc_ring.last_finalized_seq, 0);
 
 	rb->text_data_ring.size_bits = textbits;
 	rb->text_data_ring.data = text_buf;
diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h
index 18cd25e489b89..b48b44ecbe6da 100644
--- a/kernel/printk/printk_ringbuffer.h
+++ b/kernel/printk/printk_ringbuffer.h
@@ -75,7 +75,7 @@ struct prb_desc_ring {
 	struct printk_info	*infos;
 	atomic_long_t		head_id;
 	atomic_long_t		tail_id;
-	atomic_long_t		last_finalized_id;
+	atomic_long_t		last_finalized_seq;
 };
 
 /*
@@ -127,8 +127,22 @@ enum desc_state {
 #define DESC_SV(id, state)	(((unsigned long)state << DESC_FLAGS_SHIFT) | id)
 #define DESC_ID_MASK		(~DESC_FLAGS_MASK)
 #define DESC_ID(sv)		((sv) & DESC_ID_MASK)
+
+/*
+ * Special data block logical position values (for fields of
+ * @prb_desc.text_blk_lpos).
+ *
+ * - Bit0 is used to identify if the record has no data block. (Implemented in
+ *   the LPOS_DATALESS() macro.)
+ *
+ * - Bit1 specifies the reason for not having a data block.
+ *
+ * These special values could never be real lpos values because of the
+ * meta data and alignment padding of data blocks. (See to_blk_size() for
+ * details.)
+ */
 #define FAILED_LPOS		0x1
-#define NO_LPOS			0x3
+#define EMPTY_LINE_LPOS		0x3
 
 #define FAILED_BLK_LPOS	\
 {				\
@@ -259,7 +273,7 @@ static struct printk_ringbuffer name = {							\
 		.infos		= &_##name##_infos[0],						\
 		.head_id	= ATOMIC_INIT(DESC0_ID(descbits)),				\
 		.tail_id	= ATOMIC_INIT(DESC0_ID(descbits)),				\
-		.last_finalized_id = ATOMIC_INIT(DESC0_ID(descbits)),				\
+		.last_finalized_seq = ATOMIC_INIT(0),						\
 	},											\
 	.text_data_ring = {									\
 		.size_bits	= (avgtextbits) + (descbits),					\
@@ -380,5 +394,6 @@ bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq,
 
 u64 prb_first_valid_seq(struct printk_ringbuffer *rb);
 u64 prb_next_seq(struct printk_ringbuffer *rb);
+u64 prb_next_reserve_seq(struct printk_ringbuffer *rb);
 
 #endif /* _KERNEL_PRINTK_RINGBUFFER_H */
diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index 6d10927a07d83..8d9408d653de5 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -26,6 +26,18 @@ void __printk_safe_exit(void)
 	this_cpu_dec(printk_context);
 }
 
+void __printk_deferred_enter(void)
+{
+	cant_migrate();
+	this_cpu_inc(printk_context);
+}
+
+void __printk_deferred_exit(void)
+{
+	cant_migrate();
+	this_cpu_dec(printk_context);
+}
+
 asmlinkage int vprintk(const char *fmt, va_list args)
 {
 #ifdef CONFIG_KGDB_KDB
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 30fc9d34e3297..a0b0358352de0 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -2409,6 +2409,12 @@ static int rcutorture_booster_init(unsigned int cpu)
 		WARN_ON_ONCE(!t);
 		sp.sched_priority = 2;
 		sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+#ifdef CONFIG_PREEMPT_RT
+		t = per_cpu(timersd, cpu);
+		WARN_ON_ONCE(!t);
+		sp.sched_priority = 2;
+		sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+#endif
 	}
 
 	/* Don't allow time recalculation while creating a new task. */
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index ac8e86babe449..efb2be8939a2d 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -9,6 +9,7 @@
 
 #include <linux/kvm_para.h>
 #include <linux/rcu_notifier.h>
+#include <linux/console.h>
 
 //////////////////////////////////////////////////////////////////////////////
 //
@@ -604,6 +605,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 	if (rcu_stall_is_suppressed())
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	/*
 	 * OK, time to rat on our buddy...
 	 * See Documentation/RCU/stallwarn.rst for info on how to debug
@@ -658,6 +661,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 	panic_on_rcu_stall();
 
 	rcu_force_quiescent_state();  /* Kick them all. */
+
+	nbcon_cpu_emergency_exit();
 }
 
 static void print_cpu_stall(unsigned long gps)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a708d225c28e8..d0db38a6978a5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -898,14 +898,15 @@ static inline void hrtick_rq_init(struct rq *rq)
 
 #if defined(CONFIG_SMP) && defined(TIF_POLLING_NRFLAG)
 /*
- * Atomically set TIF_NEED_RESCHED and test for TIF_POLLING_NRFLAG,
+ * Atomically set TIF_NEED_RESCHED[_LAZY] and test for TIF_POLLING_NRFLAG,
  * this avoids any races wrt polling state changes and thereby avoids
  * spurious IPIs.
  */
-static inline bool set_nr_and_not_polling(struct task_struct *p)
+static inline bool set_nr_and_not_polling(struct task_struct *p, int tif_bit)
 {
 	struct thread_info *ti = task_thread_info(p);
-	return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLAG);
+
+	return !(fetch_or(&ti->flags, 1 << tif_bit) & _TIF_POLLING_NRFLAG);
 }
 
 /*
@@ -922,7 +923,7 @@ static bool set_nr_if_polling(struct task_struct *p)
 	do {
 		if (!(val & _TIF_POLLING_NRFLAG))
 			return false;
-		if (val & _TIF_NEED_RESCHED)
+		if (val & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY))
 			return true;
 	} while (!try_cmpxchg(&ti->flags, &val, val | _TIF_NEED_RESCHED));
 
@@ -930,9 +931,9 @@ static bool set_nr_if_polling(struct task_struct *p)
 }
 
 #else
-static inline bool set_nr_and_not_polling(struct task_struct *p)
+static inline bool set_nr_and_not_polling(struct task_struct *p, int tif_bit)
 {
-	set_tsk_need_resched(p);
+	set_tsk_thread_flag(p, tif_bit);
 	return true;
 }
 
@@ -1037,28 +1038,47 @@ void wake_up_q(struct wake_q_head *head)
  * might also involve a cross-CPU call to trigger the scheduler on
  * the target CPU.
  */
-void resched_curr(struct rq *rq)
+static void __resched_curr(struct rq *rq, int lazy)
 {
+	int cpu, tif_bit = TIF_NEED_RESCHED + lazy;
 	struct task_struct *curr = rq->curr;
-	int cpu;
 
 	lockdep_assert_rq_held(rq);
 
-	if (test_tsk_need_resched(curr))
+	if (unlikely(test_tsk_thread_flag(curr, tif_bit)))
 		return;
 
 	cpu = cpu_of(rq);
 
 	if (cpu == smp_processor_id()) {
-		set_tsk_need_resched(curr);
-		set_preempt_need_resched();
+		set_tsk_thread_flag(curr, tif_bit);
+		if (!lazy)
+			set_preempt_need_resched();
 		return;
 	}
 
-	if (set_nr_and_not_polling(curr))
-		smp_send_reschedule(cpu);
-	else
+	if (set_nr_and_not_polling(curr, tif_bit)) {
+		if (!lazy)
+			smp_send_reschedule(cpu);
+	} else {
 		trace_sched_wake_idle_without_ipi(cpu);
+	}
+}
+
+void resched_curr(struct rq *rq)
+{
+	__resched_curr(rq, 0);
+}
+
+void resched_curr_lazy(struct rq *rq)
+{
+	int lazy = IS_ENABLED(CONFIG_PREEMPT_BUILD_AUTO) && !sched_feat(FORCE_NEED_RESCHED) ?
+		TIF_NEED_RESCHED_LAZY_OFFSET : 0;
+
+	if (lazy && unlikely(test_tsk_thread_flag(rq->curr, TIF_NEED_RESCHED)))
+		return;
+
+	__resched_curr(rq, lazy);
 }
 
 void resched_cpu(int cpu)
@@ -1131,7 +1151,7 @@ static void wake_up_idle_cpu(int cpu)
 	if (cpu == smp_processor_id())
 		return;
 
-	if (set_nr_and_not_polling(rq->idle))
+	if (set_nr_and_not_polling(rq->idle, TIF_NEED_RESCHED))
 		smp_send_reschedule(cpu);
 	else
 		trace_sched_wake_idle_without_ipi(cpu);
@@ -8865,6 +8885,21 @@ static inline void preempt_dynamic_init(void) { }
 
 #endif /* #ifdef CONFIG_PREEMPT_DYNAMIC */
 
+/*
+ * task_is_pi_boosted - Check if task has been PI boosted.
+ * @p:	Task to check.
+ *
+ * Return true if task is subject to priority inheritance.
+ */
+bool task_is_pi_boosted(const struct task_struct *p)
+{
+	int prio = p->prio;
+
+	if (!rt_prio(prio))
+		return false;
+	return prio != p->normal_prio;
+}
+
 /**
  * yield - yield the current processor to other threads.
  *
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 4580a450700ec..b40a080e5272d 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -333,6 +333,23 @@ static const struct file_operations sched_debug_fops = {
 	.release	= seq_release,
 };
 
+static ssize_t sched_hog_write(struct file *filp, const char __user *ubuf,
+			       size_t cnt, loff_t *ppos)
+{
+	unsigned long end = jiffies + 60 * HZ;
+
+	for (; time_before(jiffies, end) && !signal_pending(current);)
+		cpu_relax();
+
+	return cnt;
+}
+
+static const struct file_operations sched_hog_fops = {
+	.write		= sched_hog_write,
+	.open		= simple_open,
+	.llseek		= default_llseek,
+};
+
 static struct dentry *debugfs_sched;
 
 static __init int sched_init_debug(void)
@@ -374,6 +391,8 @@ static __init int sched_init_debug(void)
 
 	debugfs_create_file("debug", 0444, debugfs_sched, NULL, &sched_debug_fops);
 
+	debugfs_create_file("hog", 0200, debugfs_sched, NULL, &sched_hog_fops);
+
 	return 0;
 }
 late_initcall(sched_init_debug);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d7a3c63a2171a..a2ca9589880a1 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1001,8 +1001,10 @@ static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se);
  * XXX: strictly: vd_i += N*r_i/w_i such that: vd_i > ve_i
  * this is probably good enough.
  */
-static void update_deadline(struct cfs_rq *cfs_rq, struct sched_entity *se)
+static void update_deadline(struct cfs_rq *cfs_rq, struct sched_entity *se, bool tick)
 {
+	struct rq *rq = rq_of(cfs_rq);
+
 	if ((s64)(se->vruntime - se->deadline) < 0)
 		return;
 
@@ -1021,10 +1023,19 @@ static void update_deadline(struct cfs_rq *cfs_rq, struct sched_entity *se)
 	/*
 	 * The task has consumed its request, reschedule.
 	 */
-	if (cfs_rq->nr_running > 1) {
-		resched_curr(rq_of(cfs_rq));
-		clear_buddies(cfs_rq, se);
+	if (cfs_rq->nr_running < 2)
+		return;
+
+	if (!IS_ENABLED(CONFIG_PREEMPT_BUILD_AUTO) || sched_feat(FORCE_NEED_RESCHED)) {
+		resched_curr(rq);
+	} else {
+		/* Did the task ignore the lazy reschedule request? */
+		if (tick && test_tsk_thread_flag(rq->curr, TIF_NEED_RESCHED_LAZY))
+			resched_curr(rq);
+		else
+			resched_curr_lazy(rq);
 	}
+	clear_buddies(cfs_rq, se);
 }
 
 #include "pelt.h"
@@ -1132,7 +1143,7 @@ static void update_tg_load_avg(struct cfs_rq *cfs_rq)
 /*
  * Update the current task's runtime statistics.
  */
-static void update_curr(struct cfs_rq *cfs_rq)
+static void __update_curr(struct cfs_rq *cfs_rq, bool tick)
 {
 	struct sched_entity *curr = cfs_rq->curr;
 	u64 now = rq_clock_task(rq_of(cfs_rq));
@@ -1159,7 +1170,7 @@ static void update_curr(struct cfs_rq *cfs_rq)
 	schedstat_add(cfs_rq->exec_clock, delta_exec);
 
 	curr->vruntime += calc_delta_fair(delta_exec, curr);
-	update_deadline(cfs_rq, curr);
+	update_deadline(cfs_rq, curr, tick);
 	update_min_vruntime(cfs_rq);
 
 	if (entity_is_task(curr)) {
@@ -1173,6 +1184,11 @@ static void update_curr(struct cfs_rq *cfs_rq)
 	account_cfs_rq_runtime(cfs_rq, delta_exec);
 }
 
+static inline void update_curr(struct cfs_rq *cfs_rq)
+{
+	__update_curr(cfs_rq, false);
+}
+
 static void update_curr_fair(struct rq *rq)
 {
 	update_curr(cfs_rq_of(&rq->curr->se));
@@ -5449,7 +5465,7 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
 	/*
 	 * Update run-time statistics of the 'current'.
 	 */
-	update_curr(cfs_rq);
+	__update_curr(cfs_rq, true);
 
 	/*
 	 * Ensure that runnable average is periodically updated.
@@ -5463,7 +5479,7 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
 	 * validating it and just reschedule.
 	 */
 	if (queued) {
-		resched_curr(rq_of(cfs_rq));
+		resched_curr_lazy(rq_of(cfs_rq));
 		return;
 	}
 	/*
@@ -5609,7 +5625,7 @@ static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
 	 * hierarchy can be throttled
 	 */
 	if (!assign_cfs_rq_runtime(cfs_rq) && likely(cfs_rq->curr))
-		resched_curr(rq_of(cfs_rq));
+		resched_curr_lazy(rq_of(cfs_rq));
 }
 
 static __always_inline
@@ -5869,7 +5885,7 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 
 	/* Determine whether we need to wake up potentially idle CPU: */
 	if (rq->curr == rq->idle && rq->cfs.nr_running)
-		resched_curr(rq);
+		resched_curr_lazy(rq);
 }
 
 #ifdef CONFIG_SMP
@@ -6584,7 +6600,7 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
 
 		if (delta < 0) {
 			if (task_current(rq, p))
-				resched_curr(rq);
+				resched_curr_lazy(rq);
 			return;
 		}
 		hrtick_start(rq, delta);
@@ -8240,7 +8256,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
 	 * prevents us from potentially nominating it as a false LAST_BUDDY
 	 * below.
 	 */
-	if (test_tsk_need_resched(curr))
+	if (need_resched())
 		return;
 
 	/* Idle tasks are by definition preempted by non-idle tasks. */
@@ -8282,7 +8298,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
 	return;
 
 preempt:
-	resched_curr(rq);
+	resched_curr_lazy(rq);
 }
 
 #ifdef CONFIG_SMP
@@ -12449,7 +12465,7 @@ static inline void task_tick_core(struct rq *rq, struct task_struct *curr)
 	 */
 	if (rq->core->core_forceidle_count && rq->cfs.nr_running == 1 &&
 	    __entity_slice_used(&curr->se, MIN_NR_TASKS_DURING_FORCEIDLE))
-		resched_curr(rq);
+		resched_curr_lazy(rq);
 }
 
 /*
@@ -12614,7 +12630,7 @@ prio_changed_fair(struct rq *rq, struct task_struct *p, int oldprio)
 	 */
 	if (task_current(rq, p)) {
 		if (p->prio > oldprio)
-			resched_curr(rq);
+			resched_curr_lazy(rq);
 	} else
 		wakeup_preempt(rq, p, 0);
 }
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index a3ddf84de430f..c3f7142ff1f84 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -88,3 +88,5 @@ SCHED_FEAT(UTIL_EST_FASTUP, true)
 SCHED_FEAT(LATENCY_WARN, false)
 
 SCHED_FEAT(HZ_BW, true)
+
+SCHED_FEAT(FORCE_NEED_RESCHED, false)
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 565f8374ddbbf..22d70000ab595 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -57,8 +57,7 @@ static noinline int __cpuidle cpu_idle_poll(void)
 	ct_cpuidle_enter();
 
 	raw_local_irq_enable();
-	while (!tif_need_resched() &&
-	       (cpu_idle_force_poll || tick_check_broadcast_expired()))
+	while (!need_resched() && (cpu_idle_force_poll || tick_check_broadcast_expired()))
 		cpu_relax();
 	raw_local_irq_disable();
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 6aaf0a3d6081d..46a1784a49f7e 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2203,8 +2203,11 @@ static int rto_next_cpu(struct root_domain *rd)
 
 		rd->rto_cpu = cpu;
 
-		if (cpu < nr_cpu_ids)
+		if (cpu < nr_cpu_ids) {
+			if (!has_pushable_tasks(cpu_rq(cpu)))
+				continue;
 			return cpu;
+		}
 
 		rd->rto_cpu = -1;
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 2e5a95486a422..68989416d046c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2419,6 +2419,7 @@ extern void init_sched_fair_class(void);
 extern void reweight_task(struct task_struct *p, int prio);
 
 extern void resched_curr(struct rq *rq);
+extern void resched_curr_lazy(struct rq *rq);
 extern void resched_cpu(int cpu);
 
 extern struct rt_bandwidth def_rt_bandwidth;
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 210cf5f8d92c2..cae0ae2e2b0bb 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -247,6 +247,19 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
 }
 EXPORT_SYMBOL(__local_bh_enable_ip);
 
+void softirq_preempt(void)
+{
+	if (WARN_ON_ONCE(!preemptible()))
+		return;
+
+	if (WARN_ON_ONCE(__this_cpu_read(softirq_ctrl.cnt) != SOFTIRQ_OFFSET))
+		return;
+
+	__local_bh_enable(SOFTIRQ_OFFSET, true);
+	/* preemption point */
+	__local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
+}
+
 /*
  * Invoked from ksoftirqd_run() outside of the interrupt disabled section
  * to acquire the per CPU local lock for reentrancy protection.
@@ -619,6 +632,24 @@ static inline void tick_irq_exit(void)
 #endif
 }
 
+#ifdef CONFIG_PREEMPT_RT
+DEFINE_PER_CPU(struct task_struct *, timersd);
+DEFINE_PER_CPU(unsigned long, pending_timer_softirq);
+
+static void wake_timersd(void)
+{
+        struct task_struct *tsk = __this_cpu_read(timersd);
+
+        if (tsk)
+                wake_up_process(tsk);
+}
+
+#else
+
+static inline void wake_timersd(void) { }
+
+#endif
+
 static inline void __irq_exit_rcu(void)
 {
 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
@@ -631,6 +662,10 @@ static inline void __irq_exit_rcu(void)
 	if (!in_interrupt() && local_softirq_pending())
 		invoke_softirq();
 
+	if (IS_ENABLED(CONFIG_PREEMPT_RT) && local_pending_timers() &&
+	    !(in_nmi() | in_hardirq()))
+		wake_timersd();
+
 	tick_irq_exit();
 }
 
@@ -963,12 +998,70 @@ static struct smp_hotplug_thread softirq_threads = {
 	.thread_comm		= "ksoftirqd/%u",
 };
 
+#ifdef CONFIG_PREEMPT_RT
+static void timersd_setup(unsigned int cpu)
+{
+        sched_set_fifo_low(current);
+}
+
+static int timersd_should_run(unsigned int cpu)
+{
+        return local_pending_timers();
+}
+
+static void run_timersd(unsigned int cpu)
+{
+	unsigned int timer_si;
+
+	ksoftirqd_run_begin();
+
+	timer_si = local_pending_timers();
+	__this_cpu_write(pending_timer_softirq, 0);
+	or_softirq_pending(timer_si);
+
+	__do_softirq();
+
+	ksoftirqd_run_end();
+}
+
+static void raise_ktimers_thread(unsigned int nr)
+{
+	trace_softirq_raise(nr);
+	__this_cpu_or(pending_timer_softirq, 1 << nr);
+}
+
+void raise_hrtimer_softirq(void)
+{
+	raise_ktimers_thread(HRTIMER_SOFTIRQ);
+}
+
+void raise_timer_softirq(void)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	raise_ktimers_thread(TIMER_SOFTIRQ);
+	wake_timersd();
+	local_irq_restore(flags);
+}
+
+static struct smp_hotplug_thread timer_threads = {
+        .store                  = &timersd,
+        .setup                  = timersd_setup,
+        .thread_should_run      = timersd_should_run,
+        .thread_fn              = run_timersd,
+        .thread_comm            = "ktimers/%u",
+};
+#endif
+
 static __init int spawn_ksoftirqd(void)
 {
 	cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD, "softirq:dead", NULL,
 				  takeover_tasklets);
 	BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
-
+#ifdef CONFIG_PREEMPT_RT
+	BUG_ON(smpboot_register_percpu_thread(&timer_threads));
+#endif
 	return 0;
 }
 early_initcall(spawn_ksoftirqd);
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 760793998cdd7..9f4d7ab03e398 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1808,7 +1808,7 @@ void hrtimer_interrupt(struct clock_event_device *dev)
 	if (!ktime_before(now, cpu_base->softirq_expires_next)) {
 		cpu_base->softirq_expires_next = KTIME_MAX;
 		cpu_base->softirq_activated = 1;
-		raise_softirq_irqoff(HRTIMER_SOFTIRQ);
+		raise_hrtimer_softirq();
 	}
 
 	__hrtimer_run_queues(cpu_base, now, flags, HRTIMER_ACTIVE_HARD);
@@ -1921,7 +1921,7 @@ void hrtimer_run_queues(void)
 	if (!ktime_before(now, cpu_base->softirq_expires_next)) {
 		cpu_base->softirq_expires_next = KTIME_MAX;
 		cpu_base->softirq_activated = 1;
-		raise_softirq_irqoff(HRTIMER_SOFTIRQ);
+		raise_hrtimer_softirq();
 	}
 
 	__hrtimer_run_queues(cpu_base, now, flags, HRTIMER_ACTIVE_HARD);
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index be77b021e5d63..547acecec6de6 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -796,7 +796,7 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
 
 static inline bool local_timer_softirq_pending(void)
 {
-	return local_softirq_pending() & BIT(TIMER_SOFTIRQ);
+	return local_pending_timers() & BIT(TIMER_SOFTIRQ);
 }
 
 static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 63a8ce7177dd4..b3fbe97d1e342 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1470,9 +1470,16 @@ static inline void timer_base_unlock_expiry(struct timer_base *base)
  */
 static void timer_sync_wait_running(struct timer_base *base)
 {
-	if (atomic_read(&base->timer_waiters)) {
+	bool need_preempt;
+
+	need_preempt = task_is_pi_boosted(current);
+	if (need_preempt || atomic_read(&base->timer_waiters)) {
 		raw_spin_unlock_irq(&base->lock);
 		spin_unlock(&base->expiry_lock);
+
+		if (need_preempt)
+			softirq_preempt();
+
 		spin_lock(&base->expiry_lock);
 		raw_spin_lock_irq(&base->lock);
 	}
@@ -2054,7 +2061,7 @@ static void run_local_timers(void)
 		if (time_before(jiffies, base->next_expiry))
 			return;
 	}
-	raise_softirq(TIMER_SOFTIRQ);
+	raise_timer_softirq();
 }
 
 /*
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 9aebf904ff973..87f8e4d1edeb5 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2723,6 +2723,8 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status)
 
 	if (tif_need_resched())
 		trace_flags |= TRACE_FLAG_NEED_RESCHED;
+	if (tif_need_resched_lazy())
+		trace_flags |= TRACE_FLAG_NEED_RESCHED_LAZY;
 	if (test_preempt_need_resched())
 		trace_flags |= TRACE_FLAG_PREEMPT_RESCHED;
 	return (trace_flags << 16) | (min_t(unsigned int, pc & 0xff, 0xf)) |
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index d8b302d010830..4f58a196e14c1 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -460,17 +460,29 @@ int trace_print_lat_fmt(struct trace_seq *s, struct trace_entry *entry)
 		(entry->flags & TRACE_FLAG_IRQS_OFF && bh_off) ? 'D' :
 		(entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' :
 		bh_off ? 'b' :
-		(entry->flags & TRACE_FLAG_IRQS_NOSUPPORT) ? 'X' :
+		!IS_ENABLED(CONFIG_TRACE_IRQFLAGS_SUPPORT) ? 'X' :
 		'.';
 
-	switch (entry->flags & (TRACE_FLAG_NEED_RESCHED |
+	switch (entry->flags & (TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY |
 				TRACE_FLAG_PREEMPT_RESCHED)) {
+	case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY | TRACE_FLAG_PREEMPT_RESCHED:
+		need_resched = 'B';
+		break;
 	case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_PREEMPT_RESCHED:
 		need_resched = 'N';
 		break;
+	case TRACE_FLAG_NEED_RESCHED_LAZY | TRACE_FLAG_PREEMPT_RESCHED:
+		need_resched = 'L';
+		break;
+	case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY:
+		need_resched = 'b';
+		break;
 	case TRACE_FLAG_NEED_RESCHED:
 		need_resched = 'n';
 		break;
+	case TRACE_FLAG_NEED_RESCHED_LAZY:
+		need_resched = 'l';
+		break;
 	case TRACE_FLAG_PREEMPT_RESCHED:
 		need_resched = 'p';
 		break;
diff --git a/localversion-rt b/localversion-rt
new file mode 100644
index 0000000000000..6f206be67cd28
--- /dev/null
+++ b/localversion-rt
@@ -0,0 +1 @@
+-rt1
diff --git a/net/core/dev.c b/net/core/dev.c
index af53f6d838ce9..615017b1965c3 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4679,15 +4679,6 @@ static void rps_trigger_softirq(void *data)
 
 #endif /* CONFIG_RPS */
 
-/* Called from hardirq (IPI) context */
-static void trigger_rx_softirq(void *data)
-{
-	struct softnet_data *sd = data;
-
-	__raise_softirq_irqoff(NET_RX_SOFTIRQ);
-	smp_store_release(&sd->defer_ipi_scheduled, 0);
-}
-
 /*
  * After we queued a packet into sd->input_pkt_queue,
  * we need to make sure this queue is serviced soon.
@@ -6658,6 +6649,32 @@ static void skb_defer_free_flush(struct softnet_data *sd)
 	}
 }
 
+#ifndef CONFIG_PREEMPT_RT
+
+/* Called from hardirq (IPI) context */
+static void trigger_rx_softirq(void *data)
+{
+	struct softnet_data *sd = data;
+
+	__raise_softirq_irqoff(NET_RX_SOFTIRQ);
+	smp_store_release(&sd->defer_ipi_scheduled, 0);
+}
+
+#else
+
+static void trigger_rx_softirq(struct work_struct *defer_work)
+{
+	struct softnet_data *sd;
+
+	sd = container_of(defer_work, struct softnet_data, defer_work);
+	smp_store_release(&sd->defer_ipi_scheduled, 0);
+	local_bh_disable();
+	skb_defer_free_flush(sd);
+	local_bh_enable();
+}
+
+#endif
+
 static int napi_threaded_poll(void *data)
 {
 	struct napi_struct *napi = data;
@@ -11566,7 +11583,11 @@ static int __init net_dev_init(void)
 		INIT_CSD(&sd->csd, rps_trigger_softirq, sd);
 		sd->cpu = i;
 #endif
+#ifndef CONFIG_PREEMPT_RT
 		INIT_CSD(&sd->defer_csd, trigger_rx_softirq, sd);
+#else
+		INIT_WORK(&sd->defer_work, trigger_rx_softirq);
+#endif
 		spin_lock_init(&sd->defer_lock);
 
 		init_gro_hash(&sd->backlog);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index b157efea5dea8..251ebf3fefac3 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -6858,8 +6858,13 @@ nodefer:	__kfree_skb(skb);
 	/* Make sure to trigger NET_RX_SOFTIRQ on the remote CPU
 	 * if we are unlucky enough (this seems very unlikely).
 	 */
-	if (unlikely(kick) && !cmpxchg(&sd->defer_ipi_scheduled, 0, 1))
+	if (unlikely(kick) && !cmpxchg(&sd->defer_ipi_scheduled, 0, 1)) {
+#ifndef CONFIG_PREEMPT_RT
 		smp_call_function_single_async(cpu, &sd->defer_csd);
+#else
+		schedule_work_on(cpu, &sd->defer_work);
+#endif
+	}
 }
 
 static void skb_splice_csum_page(struct sk_buff *skb, struct page *page,
