Merge tag 'printk-for-5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

Pull printk updates from Petr Mladek:

 - Optionally, provide an index of possible printk messages via
   <debugfs>/printk/index/. It can be used when monitoring important
   kernel messages on a farm of various hosts. The monitor has to be
   updated when some messages has changed or are not longer available by
   a newly deployed kernel.

 - Add printk.console_no_auto_verbose boot parameter. It allows to
   generate crash dump even with slow consoles in a reasonable time
   frame.

 - Remove printk_safe buffers. The messages are always stored directly
   to the main logbuffer, even in NMI or recursive context. Also it
   allows to serialize syslog operations by a mutex instead of a spin
   lock.

 - Misc clean up and build fixes.

* tag 'printk-for-5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
  printk/index: Fix -Wunused-function warning
  lib/nmi_backtrace: Serialize even messages about idle CPUs
  printk: Add printk.console_no_auto_verbose boot parameter
  printk: Remove console_silent()
  lib/test_scanf: Handle n_bits == 0 in random tests
  printk: syslog: close window between wait and read
  printk: convert @syslog_lock to mutex
  printk: remove NMI tracking
  printk: remove safe buffers
  printk: track/limit recursion
  lib/nmi_backtrace: explicitly serialize banner and regs
  printk: Move the printk() kerneldoc comment to its new home
  printk/index: Fix warning about missing prototypes
  MIPS/asm/printk: Fix build failure caused by printk
  printk: index: Add indexing support to dev_printk
  printk: Userspace format indexing support
  printk: Rework parse_prefix into printk_parse_prefix
  printk: Straighten out log_flags into printk_info_flags
  string_helpers: Escape double quotes in escape_special
  printk/console: Check consistent sequence number when handling race in console_unlock()

38 files changed, 687 insertions, 657 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 82c932105d31..84dc5790741b 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4198,6 +4198,15 @@
 			Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
 			default: disabled
 
+	printk.console_no_auto_verbose=
+			Disable console loglevel raise on oops, panic
+			or lockdep-detected issues (only if lock debug is on).
+			With an exception to setups with low baudrate on
+			serial console, keeping this 0 is a good choice
+			in order to provide more debug information.
+			Format: <bool>
+			default: 0 (auto_verbose is enabled)
+
 	printk.devkmsg={on,off,ratelimit}
 			Control writing to /dev/kmsg.
 			on - unlimited logging to /dev/kmsg from userspace
diff --git a/Documentation/core-api/printk-basics.rst b/Documentation/core-api/printk-basics.rst
index 965e4281eddd..2dde24ca7d9f 100644
--- a/Documentation/core-api/printk-basics.rst
+++ b/Documentation/core-api/printk-basics.rst
@@ -107,9 +107,6 @@ also ``CONFIG_DYNAMIC_DEBUG`` in the case of pr_debug()) is defined.
 Function reference
 ==================
 
-.. kernel-doc:: kernel/printk/printk.c
-   :functions: printk
-
 .. kernel-doc:: include/linux/printk.h
-   :functions: pr_emerg pr_alert pr_crit pr_err pr_warn pr_notice pr_info
+   :functions: printk pr_emerg pr_alert pr_crit pr_err pr_warn pr_notice pr_info
       pr_fmt pr_debug pr_devel pr_cont
diff --git a/MAINTAINERS b/MAINTAINERS
index 63bddf7b6bf2..0d4b8963f17b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15021,6 +15021,11 @@ S:	Maintained
 F:	include/linux/printk.h
 F:	kernel/printk/
 
+PRINTK INDEXING
+R:	Chris Down <chris@chrisdown.name>
+S:	Maintained
+F:	kernel/printk/index.c
+
 PROC FILESYSTEM
 L:	linux-kernel@vger.kernel.org
 L:	linux-fsdevel@vger.kernel.org
diff --git a/arch/arm/kernel/entry-v7m.S b/arch/arm/kernel/entry-v7m.S
index d0e898608d30..7bde93c10962 100644
--- a/arch/arm/kernel/entry-v7m.S
+++ b/arch/arm/kernel/entry-v7m.S
@@ -23,7 +23,7 @@ __invalid_entry:
 	adr	r0, strerr
 	mrs	r1, ipsr
 	mov	r2, lr
-	bl	printk
+	bl	_printk
 #endif
 	mov	r0, sp
 	bl	show_regs
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index c7bb168b0d97..842427ff2b3c 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -667,9 +667,9 @@ static void do_handle_IPI(int ipinr)
 		break;
 
 	case IPI_CPU_BACKTRACE:
-		printk_nmi_enter();
+		printk_deferred_enter();
 		nmi_cpu_backtrace(get_irq_regs());
-		printk_nmi_exit();
+		printk_deferred_exit();
 		break;
 
 	default:
diff --git a/arch/arm/lib/backtrace-clang.S b/arch/arm/lib/backtrace-clang.S
index 6174c45f53a5..5b2cdb1003e3 100644
--- a/arch/arm/lib/backtrace-clang.S
+++ b/arch/arm/lib/backtrace-clang.S
@@ -202,7 +202,7 @@ finished_setup:
 1006:		adr	r0, .Lbad
 		mov	r1, loglvl
 		mov	r2, frame
-		bl	printk
+		bl	_printk
 no_frame:	ldmfd	sp!, {r4 - r9, fp, pc}
 ENDPROC(c_backtrace)
 		.pushsection __ex_table,"a"
diff --git a/arch/arm/lib/backtrace.S b/arch/arm/lib/backtrace.S
index 872f658638d9..e8408f22d4dc 100644
--- a/arch/arm/lib/backtrace.S
+++ b/arch/arm/lib/backtrace.S
@@ -103,7 +103,7 @@ for_each_frame:	tst	frame, mask		@ Check for address exceptions
 1006:		adr	r0, .Lbad
 		mov	r1, loglvl
 		mov	r2, frame
-		bl	printk
+		bl	_printk
 no_frame:	ldmfd	sp!, {r4 - r9, pc}
 ENDPROC(c_backtrace)
 		
diff --git a/arch/arm/mach-rpc/io-acorn.S b/arch/arm/mach-rpc/io-acorn.S
index b9082a2a2a01..aa9bf0d771c0 100644
--- a/arch/arm/mach-rpc/io-acorn.S
+++ b/arch/arm/mach-rpc/io-acorn.S
@@ -25,4 +25,4 @@ ENTRY(insl)
 ENTRY(outsl)
 		adr	r0, .Liosl_warning
 		mov	r1, lr
-		b	printk
+		b	_printk
diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
index d5837bf05a9a..6f7926c9c179 100644
--- a/arch/arm/vfp/vfphw.S
+++ b/arch/arm/vfp/vfphw.S
@@ -23,7 +23,7 @@
 #ifdef DEBUG
 	stmfd	sp!, {r0-r3, ip, lr}
 	ldr	r0, =1f
-	bl	printk
+	bl	_printk
 	ldmfd	sp!, {r0-r3, ip, lr}
 
 	.pushsection .rodata, "a"
@@ -38,7 +38,7 @@
 	stmfd	sp!, {r0-r3, ip, lr}
 	mov	r1, \arg
 	ldr	r0, =1f
-	bl	printk
+	bl	_printk
 	ldmfd	sp!, {r0-r3, ip, lr}
 
 	.pushsection .rodata, "a"
@@ -55,7 +55,7 @@
 	mov	r2, \arg2
 	mov	r1, \arg1
 	ldr	r0, =1f
-	bl	printk
+	bl	_printk
 	ldmfd	sp!, {r0-r3, ip, lr}
 
 	.pushsection .rodata, "a"
diff --git a/arch/ia64/include/uapi/asm/cmpxchg.h b/arch/ia64/include/uapi/asm/cmpxchg.h
index 926c6cb1e029..2c2f3cfeaa77 100644
--- a/arch/ia64/include/uapi/asm/cmpxchg.h
+++ b/arch/ia64/include/uapi/asm/cmpxchg.h
@@ -143,9 +143,9 @@ extern long ia64_cmpxchg_called_with_bad_pointer(void);
 do {									\
 	if (_cmpxchg_bugcheck_count-- <= 0) {				\
 		void *ip;						\
-		extern int printk(const char *fmt, ...);		\
+		extern int _printk(const char *fmt, ...);		\
 		ip = (void *) ia64_getreg(_IA64_REG_IP);		\
-		printk("CMPXCHG_BUGCHECK: stuck at %p on word %p\n", ip, (v));\
+		_printk("CMPXCHG_BUGCHECK: stuck at %p on word %p\n", ip, (v));\
 		break;							\
 	}								\
 } while (0)
diff --git a/arch/mips/include/asm/asm.h b/arch/mips/include/asm/asm.h
index ea4b62ece336..2f8ce94ebaaf 100644
--- a/arch/mips/include/asm/asm.h
+++ b/arch/mips/include/asm/asm.h
@@ -114,7 +114,7 @@ symbol		=	value
 		.set	push;				\
 		.set	reorder;			\
 		PTR_LA	a0, 8f;				\
-		jal	printk;				\
+		jal	_printk;			\
 		.set	pop;				\
 		TEXT(string)
 #else
diff --git a/arch/openrisc/kernel/entry.S b/arch/openrisc/kernel/entry.S
index bc657e55c15f..947613f61d4a 100644
--- a/arch/openrisc/kernel/entry.S
+++ b/arch/openrisc/kernel/entry.S
@@ -551,7 +551,7 @@ EXCEPTION_ENTRY(_external_irq_handler)
 	l.movhi r3,hi(42f)
 	l.ori	r3,r3,lo(42f)
 	l.sw    0x0(r1),r3
-	l.jal   printk
+	l.jal   _printk
 	l.sw    0x4(r1),r4
 	l.addi  r1,r1,0x8
 
@@ -681,8 +681,8 @@ _syscall_debug:
 	l.sw    -4(r1),r27
 	l.sw    -8(r1),r11
 	l.addi  r1,r1,-8
-	l.movhi r27,hi(printk)
-	l.ori   r27,r27,lo(printk)
+	l.movhi r27,hi(_printk)
+	l.ori   r27,r27,lo(_printk)
 	l.jalr  r27
 	 l.nop
 	l.addi  r1,r1,8
diff --git a/arch/powerpc/kernel/head_fsl_booke.S b/arch/powerpc/kernel/head_fsl_booke.S
index 0f9642f36b49..9a2f4265e6d2 100644
--- a/arch/powerpc/kernel/head_fsl_booke.S
+++ b/arch/powerpc/kernel/head_fsl_booke.S
@@ -858,7 +858,7 @@ KernelSPE:
 	ori	r3,r3,87f@l
 	mr	r4,r2		/* current */
 	lwz	r5,_NIP(r1)
-	bl	printk
+	bl	_printk
 #endif
 	b	interrupt_return
 #ifdef CONFIG_PRINTK
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index d56254f05e17..cd5f633c9b1b 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -171,7 +171,6 @@ extern void panic_flush_kmsg_start(void)
 
 extern void panic_flush_kmsg_end(void)
 {
-	printk_safe_flush_on_panic();
 	kmsg_dump(KMSG_DUMP_PANIC);
 	bust_spinlocks(0);
 	debug_locks_off();
diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c
index a165635fd214..f9ea0e5357f9 100644
--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -184,11 +184,6 @@ static void watchdog_smp_panic(int cpu, u64 tb)
 
 	wd_smp_unlock(&flags);
 
-	printk_safe_flush();
-	/*
-	 * printk_safe_flush() seems to require another print
-	 * before anything actually goes out to console.
-	 */
 	if (sysctl_hardlockup_all_cpu_backtrace)
 		trigger_allbutself_cpu_backtrace();
 
diff --git a/arch/powerpc/kexec/crash.c b/arch/powerpc/kexec/crash.c
index 10f997e6bb95..22ceeeb705ab 100644
--- a/arch/powerpc/kexec/crash.c
+++ b/arch/powerpc/kexec/crash.c
@@ -313,7 +313,7 @@ void default_machine_crash_shutdown(struct pt_regs *regs)
 	int (*old_handler)(struct pt_regs *regs);
 
 	/* Avoid hardlocking with irresponsive CPU holding logbuf_lock */
-	printk_nmi_enter();
+	printk_deferred_enter();
 
 	/*
 	 * This function is only called after the system
diff --git a/arch/um/include/shared/user.h b/arch/um/include/shared/user.h
index e793e4212f0a..dd4badffdeb3 100644
--- a/arch/um/include/shared/user.h
+++ b/arch/um/include/shared/user.h
@@ -38,7 +38,8 @@ extern void panic(const char *fmt, ...)
 #define UM_KERN_CONT	KERN_CONT
 
 #ifdef UML_CONFIG_PRINTK
-extern int printk(const char *fmt, ...)
+#define printk(...) _printk(__VA_ARGS__)
+extern int _printk(const char *fmt, ...)
 	__attribute__ ((format (printf, 1, 2)));
 #else
 static inline int printk(const char *fmt, ...)
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 67f590425d90..d8c64dab0efe 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -432,7 +432,7 @@ SYM_FUNC_START(early_ignore_irq)
 	pushl 32(%esp)
 	pushl 40(%esp)
 	pushl $int_msg
-	call printk
+	call _printk
 
 	call dump_stack
 
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 3a72241b87c6..280425409b40 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -4579,8 +4579,8 @@ static void __dev_printk(const char *level, const struct device *dev,
 		printk("%s(NULL device *): %pV", level, vaf);
 }
 
-void dev_printk(const char *level, const struct device *dev,
-		const char *fmt, ...)
+void _dev_printk(const char *level, const struct device *dev,
+		 const char *fmt, ...)
 {
 	struct va_format vaf;
 	va_list args;
@@ -4594,7 +4594,7 @@ void dev_printk(const char *level, const struct device *dev,
 
 	va_end(args);
 }
-EXPORT_SYMBOL(dev_printk);
+EXPORT_SYMBOL(_dev_printk);
 
 #define define_dev_printk_level(func, kern_level)		\
 void func(const struct device *dev, const char *fmt, ...)	\
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 62669b36a772..aa50bf2959fe 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -483,6 +483,8 @@
 									\
 	TRACEDATA							\
 									\
+	PRINTK_INDEX							\
+									\
 	/* Kernel symbol table: Normal symbols */			\
 	__ksymtab         : AT(ADDR(__ksymtab) - LOAD_OFFSET) {		\
 		__start___ksymtab = .;					\
@@ -894,6 +896,17 @@
 #define TRACEDATA
 #endif
 
+#ifdef CONFIG_PRINTK_INDEX
+#define PRINTK_INDEX							\
+	.printk_index : AT(ADDR(.printk_index) - LOAD_OFFSET) {		\
+		__start_printk_index = .;				\
+		*(.printk_index)					\
+		__stop_printk_index = .;				\
+	}
+#else
+#define PRINTK_INDEX
+#endif
+
 #define NOTES								\
 	.notes : AT(ADDR(.notes) - LOAD_OFFSET) {			\
 		__start_notes = .;					\
diff --git a/include/linux/dev_printk.h b/include/linux/dev_printk.h
index 82d3d46005a1..8904063d4c9f 100644
--- a/include/linux/dev_printk.h
+++ b/include/linux/dev_printk.h
@@ -38,8 +38,8 @@ __printf(3, 4) __cold
 int dev_printk_emit(int level, const struct device *dev, const char *fmt, ...);
 
 __printf(3, 4) __cold
-void dev_printk(const char *level, const struct device *dev,
-		const char *fmt, ...);
+void _dev_printk(const char *level, const struct device *dev,
+		 const char *fmt, ...);
 __printf(2, 3) __cold
 void _dev_emerg(const struct device *dev, const char *fmt, ...);
 __printf(2, 3) __cold
@@ -69,7 +69,7 @@ static inline void __dev_printk(const char *level, const struct device *dev,
 				struct va_format *vaf)
 {}
 static inline __printf(3, 4)
-void dev_printk(const char *level, const struct device *dev,
+void _dev_printk(const char *level, const struct device *dev,
 		 const char *fmt, ...)
 {}
 
@@ -98,24 +98,56 @@ void _dev_info(const struct device *dev, const char *fmt, ...)
 #endif
 
 /*
+ * Need to take variadic arguments even though we don't use them, as dev_fmt()
+ * may only just have been expanded and may result in multiple arguments.
+ */
+#define dev_printk_index_emit(level, fmt, ...) \
+	printk_index_subsys_emit("%s %s: ", level, fmt)
+
+#define dev_printk_index_wrap(_p_func, level, dev, fmt, ...)		\
+	({								\
+		dev_printk_index_emit(level, fmt);			\
+		_p_func(dev, fmt, ##__VA_ARGS__);			\
+	})
+
+/*
+ * Some callsites directly call dev_printk rather than going through the
+ * dev_<level> infrastructure, so we need to emit here as well as inside those
+ * level-specific macros. Only one index entry will be produced, either way,
+ * since dev_printk's `fmt` isn't known at compile time if going through the
+ * dev_<level> macros.
+ *
+ * dev_fmt() isn't called for dev_printk when used directly, as it's used by
+ * the dev_<level> macros internally which already have dev_fmt() processed.
+ *
+ * We also can't use dev_printk_index_wrap directly, because we have a separate
+ * level to process.
+ */
+#define dev_printk(level, dev, fmt, ...)				\
+	({								\
+		dev_printk_index_emit(level, fmt);			\
+		_dev_printk(level, dev, fmt, ##__VA_ARGS__);		\
+	})
+
+/*
  * #defines for all the dev_<level> macros to prefix with whatever
  * possible use of #define dev_fmt(fmt) ...
  */
 
-#define dev_emerg(dev, fmt, ...)					\
-	_dev_emerg(dev, dev_fmt(fmt), ##__VA_ARGS__)
-#define dev_crit(dev, fmt, ...)						\
-	_dev_crit(dev, dev_fmt(fmt), ##__VA_ARGS__)
-#define dev_alert(dev, fmt, ...)					\
-	_dev_alert(dev, dev_fmt(fmt), ##__VA_ARGS__)
-#define dev_err(dev, fmt, ...)						\
-	_dev_err(dev, dev_fmt(fmt), ##__VA_ARGS__)
-#define dev_warn(dev, fmt, ...)						\
-	_dev_warn(dev, dev_fmt(fmt), ##__VA_ARGS__)
-#define dev_notice(dev, fmt, ...)					\
-	_dev_notice(dev, dev_fmt(fmt), ##__VA_ARGS__)
-#define dev_info(dev, fmt, ...)						\
-	_dev_info(dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_emerg(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_emerg, KERN_EMERG, dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_crit(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_crit, KERN_CRIT, dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_alert(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_alert, KERN_ALERT, dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_err(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_err, KERN_ERR, dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_warn(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_warn, KERN_WARNING, dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_notice(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_notice, KERN_NOTICE, dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_info(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_info, KERN_INFO, dev, dev_fmt(fmt), ##__VA_ARGS__)
 
 #if defined(CONFIG_DYNAMIC_DEBUG) || \
 	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 69bc86ea382c..76878b357ffa 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -116,7 +116,6 @@ extern void rcu_nmi_exit(void);
 	do {							\
 		lockdep_off();					\
 		arch_nmi_enter();				\
-		printk_nmi_enter();				\
 		BUG_ON(in_nmi() == NMI_MASK);			\
 		__preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET);	\
 	} while (0)
@@ -135,7 +134,6 @@ extern void rcu_nmi_exit(void);
 	do {							\
 		BUG_ON(!in_nmi());				\
 		__preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET);	\
-		printk_nmi_exit();				\
 		arch_nmi_exit();				\
 		lockdep_on();					\
 	} while (0)
diff --git a/include/linux/module.h b/include/linux/module.h
index 8a298d820dbc..c9f1200b2312 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -511,6 +511,11 @@ struct module {
 	struct klp_modinfo *klp_info;
 #endif
 
+#ifdef CONFIG_PRINTK_INDEX
+	unsigned int printk_index_size;
+	struct pi_entry **printk_index_start;
+#endif
+
 #ifdef CONFIG_MODULE_UNLOAD
 	/* What modules depend on me? */
 	struct list_head source_list;
diff --git a/include/linux/printk.h b/include/linux/printk.h
index e834d78f0478..259af4f97f50 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -70,16 +70,7 @@ extern int console_printk[];
 #define minimum_console_loglevel (console_printk[2])
 #define default_console_loglevel (console_printk[3])
 
-static inline void console_silent(void)
-{
-	console_loglevel = CONSOLE_LOGLEVEL_SILENT;
-}
-
-static inline void console_verbose(void)
-{
-	if (console_loglevel)
-		console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
-}
+extern void console_verbose(void);
 
 /* strlen("ratelimit") + 1 */
 #define DEVKMSG_STR_MAX_SIZE 10
@@ -150,18 +141,6 @@ static inline __printf(1, 2) __cold
 void early_printk(const char *s, ...) { }
 #endif
 
-#ifdef CONFIG_PRINTK_NMI
-extern void printk_nmi_enter(void);
-extern void printk_nmi_exit(void);
-extern void printk_nmi_direct_enter(void);
-extern void printk_nmi_direct_exit(void);
-#else
-static inline void printk_nmi_enter(void) { }
-static inline void printk_nmi_exit(void) { }
-static inline void printk_nmi_direct_enter(void) { }
-static inline void printk_nmi_direct_exit(void) { }
-#endif /* PRINTK_NMI */
-
 struct dev_printk_info;
 
 #ifdef CONFIG_PRINTK
@@ -174,12 +153,22 @@ asmlinkage __printf(1, 0)
 int vprintk(const char *fmt, va_list args);
 
 asmlinkage __printf(1, 2) __cold
-int printk(const char *fmt, ...);
+int _printk(const char *fmt, ...);
 
 /*
  * Special printk facility for scheduler/timekeeping use only, _DO_NOT_USE_ !
  */
-__printf(1, 2) __cold int printk_deferred(const char *fmt, ...);
+__printf(1, 2) __cold int _printk_deferred(const char *fmt, ...);
+
+extern void __printk_safe_enter(void);
+extern void __printk_safe_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
 
 /*
  * Please don't use printk_ratelimit(), because it shares ratelimiting state
@@ -209,8 +198,6 @@ void dump_stack_print_info(const char *log_lvl);
 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;
-extern void printk_safe_flush(void);
-extern void printk_safe_flush_on_panic(void);
 #else
 static inline __printf(1, 0)
 int vprintk(const char *s, va_list args)
@@ -218,15 +205,24 @@ int vprintk(const char *s, va_list args)
 	return 0;
 }
 static inline __printf(1, 2) __cold
-int printk(const char *s, ...)
+int _printk(const char *s, ...)
 {
 	return 0;
 }
 static inline __printf(1, 2) __cold
-int printk_deferred(const char *s, ...)
+int _printk_deferred(const char *s, ...)
 {
 	return 0;
 }
+
+static inline void printk_deferred_enter(void)
+{
+}
+
+static inline void printk_deferred_exit(void)
+{
+}
+
 static inline int printk_ratelimit(void)
 {
 	return 0;
@@ -278,14 +274,6 @@ static inline void dump_stack_lvl(const char *log_lvl)
 static inline void dump_stack(void)
 {
 }
-
-static inline void printk_safe_flush(void)
-{
-}
-
-static inline void printk_safe_flush_on_panic(void)
-{
-}
 #endif
 
 #ifdef CONFIG_SMP
@@ -348,6 +336,117 @@ extern int kptr_restrict;
 #define pr_fmt(fmt) fmt
 #endif
 
+struct module;
+
+#ifdef CONFIG_PRINTK_INDEX
+struct pi_entry {
+	const char *fmt;
+	const char *func;
+	const char *file;
+	unsigned int line;
+
+	/*
+	 * While printk and pr_* have the level stored in the string at compile
+	 * time, some subsystems dynamically add it at runtime through the
+	 * format string. For these dynamic cases, we allow the subsystem to
+	 * tell us the level at compile time.
+	 *
+	 * NULL indicates that the level, if any, is stored in fmt.
+	 */
+	const char *level;
+
+	/*
+	 * The format string used by various subsystem specific printk()
+	 * wrappers to prefix the message.
+	 *
+	 * Note that the static prefix defined by the pr_fmt() macro is stored
+	 * directly in the message format (@fmt), not here.
+	 */
+	const char *subsys_fmt_prefix;
+} __packed;
+
+#define __printk_index_emit(_fmt, _level, _subsys_fmt_prefix)		\
+	do {								\
+		if (__builtin_constant_p(_fmt) && __builtin_constant_p(_level)) { \
+			/*
+			 * We check __builtin_constant_p multiple times here
+			 * for the same input because GCC will produce an error
+			 * if we try to assign a static variable to fmt if it
+			 * is not a constant, even with the outer if statement.
+			 */						\
+			static const struct pi_entry _entry		\
+			__used = {					\
+				.fmt = __builtin_constant_p(_fmt) ? (_fmt) : NULL, \
+				.func = __func__,			\
+				.file = __FILE__,			\
+				.line = __LINE__,			\
+				.level = __builtin_constant_p(_level) ? (_level) : NULL, \
+				.subsys_fmt_prefix = _subsys_fmt_prefix,\
+			};						\
+			static const struct pi_entry *_entry_ptr	\
+			__used __section(".printk_index") = &_entry;	\
+		}							\
+	} while (0)
+
+#else /* !CONFIG_PRINTK_INDEX */
+#define __printk_index_emit(...) do {} while (0)
+#endif /* CONFIG_PRINTK_INDEX */
+
+/*
+ * Some subsystems have their own custom printk that applies a va_format to a
+ * generic format, for example, to include a device number or other metadata
+ * alongside the format supplied by the caller.
+ *
+ * In order to store these in the way they would be emitted by the printk
+ * infrastructure, the subsystem provides us with the start, fixed string, and
+ * any subsequent text in the format string.
+ *
+ * We take a variable argument list as pr_fmt/dev_fmt/etc are sometimes passed
+ * as multiple arguments (eg: `"%s: ", "blah"`), and we must only take the
+ * first one.
+ *
+ * subsys_fmt_prefix must be known at compile time, or compilation will fail
+ * (since this is a mistake). If fmt or level is not known at compile time, no
+ * index entry will be made (since this can legitimately happen).
+ */
+#define printk_index_subsys_emit(subsys_fmt_prefix, level, fmt, ...) \
+	__printk_index_emit(fmt, level, subsys_fmt_prefix)
+
+#define printk_index_wrap(_p_func, _fmt, ...)				\
+	({								\
+		__printk_index_emit(_fmt, NULL, NULL);			\
+		_p_func(_fmt, ##__VA_ARGS__);				\
+	})
+
+
+/**
+ * printk - print a kernel message
+ * @fmt: format string
+ *
+ * This is printk(). It can be called from any context. We want it to work.
+ *
+ * If printk indexing is enabled, _printk() is called from printk_index_wrap.
+ * Otherwise, printk is simply #defined to _printk.
+ *
+ * We try to grab the console_lock. If we succeed, it's easy - we log the
+ *