linuxkit/kernel/5.11.x-rt/patches/0045-0026-printk-remove-deferred-printing.patch

From: John Ogness <john.ogness@linutronix.de>
Date: Mon, 30 Nov 2020 01:42:08 +0106
Subject: [PATCH 26/28] printk: remove deferred printing

Since printing occurs either atomically or from the printing
kthread, there is no need for any deferring or tracking possible
recursion paths. Remove all printk context tracking.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 arch/arm/kernel/smp.c       |    2 -
 arch/powerpc/kexec/crash.c  |    3 -
 include/linux/hardirq.h     |    2 -
 include/linux/printk.h      |   12 ------
 kernel/printk/Makefile      |    1 
 kernel/printk/internal.h    |   70 -----------------------------------
 kernel/printk/printk.c      |   58 +++++++++++------------------
 kernel/printk/printk_safe.c |   88 --------------------------------------------
 kernel/trace/trace.c        |    2 -
 9 files changed, 22 insertions(+), 216 deletions(-)
 delete mode 100644 kernel/printk/internal.h
 delete mode 100644 kernel/printk/printk_safe.c

--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -671,9 +671,7 @@ static void do_handle_IPI(int ipinr)
 		break;
 
 	case IPI_CPU_BACKTRACE:
-		printk_nmi_enter();
 		nmi_cpu_backtrace(get_irq_regs());
-		printk_nmi_exit();
 		break;
 
 	default:
--- a/arch/powerpc/kexec/crash.c
+++ b/arch/powerpc/kexec/crash.c
@@ -311,9 +311,6 @@ void default_machine_crash_shutdown(stru
 	unsigned int i;
 	int (*old_handler)(struct pt_regs *regs);
 
-	/* Avoid hardlocking with irresponsive CPU holding logbuf_lock */
-	printk_nmi_enter();
-
 	/*
 	 * This function is only called after the system
 	 * has panicked or is otherwise in a critical state.
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -115,7 +115,6 @@ 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)
@@ -134,7 +133,6 @@ 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)
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -155,18 +155,6 @@ 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
--- a/kernel/printk/Makefile
+++ b/kernel/printk/Makefile
@@ -1,5 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-y	= printk.o
-obj-$(CONFIG_PRINTK)	+= printk_safe.o
 obj-$(CONFIG_A11Y_BRAILLE_CONSOLE)	+= braille.o
 obj-$(CONFIG_PRINTK)	+= printk_ringbuffer.o
--- a/kernel/printk/internal.h
+++ /dev/null
@@ -1,70 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-or-later */
-/*
- * internal.h - printk internal definitions
- */
-#include <linux/percpu.h>
-
-#ifdef CONFIG_PRINTK
-
-#define PRINTK_SAFE_CONTEXT_MASK	0x007ffffff
-#define PRINTK_NMI_DIRECT_CONTEXT_MASK	0x008000000
-#define PRINTK_NMI_CONTEXT_MASK		0xff0000000
-
-#define PRINTK_NMI_CONTEXT_OFFSET	0x010000000
-
-__printf(4, 0)
-int vprintk_store(int facility, int level,
-		  const struct dev_printk_info *dev_info,
-		  const char *fmt, va_list args);
-
-__printf(1, 0) int vprintk_default(const char *fmt, va_list args);
-__printf(1, 0) int vprintk_deferred(const char *fmt, va_list args);
-__printf(1, 0) int vprintk_func(const char *fmt, va_list args);
-void __printk_safe_enter(void);
-void __printk_safe_exit(void);
-
-bool printk_percpu_data_ready(void);
-
-#define printk_safe_enter_irqsave(flags)	\
-	do {					\
-		local_irq_save(flags);		\
-		__printk_safe_enter();		\
-	} while (0)
-
-#define printk_safe_exit_irqrestore(flags)	\
-	do {					\
-		__printk_safe_exit();		\
-		local_irq_restore(flags);	\
-	} while (0)
-
-#define printk_safe_enter_irq()		\
-	do {					\
-		local_irq_disable();		\
-		__printk_safe_enter();		\
-	} while (0)
-
-#define printk_safe_exit_irq()			\
-	do {					\
-		__printk_safe_exit();		\
-		local_irq_enable();		\
-	} while (0)
-
-void defer_console_output(void);
-
-#else
-
-__printf(1, 0) int vprintk_func(const char *fmt, va_list args) { return 0; }
-
-/*
- * In !PRINTK builds we still export console_sem
- * semaphore and some of console functions (console_unlock()/etc.), so
- * printk-safe must preserve the existing local IRQ guarantees.
- */
-#define printk_safe_enter_irqsave(flags) local_irq_save(flags)
-#define printk_safe_exit_irqrestore(flags) local_irq_restore(flags)
-
-#define printk_safe_enter_irq() local_irq_disable()
-#define printk_safe_exit_irq() local_irq_enable()
-
-static inline bool printk_percpu_data_ready(void) { return false; }
-#endif /* CONFIG_PRINTK */
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -45,6 +45,7 @@
 #include <linux/ctype.h>
 #include <linux/uio.h>
 #include <linux/kthread.h>
+#include <linux/kdb.h>
 #include <linux/clocksource.h>
 #include <linux/sched/clock.h>
 #include <linux/sched/debug.h>
@@ -60,7 +61,6 @@
 #include "printk_ringbuffer.h"
 #include "console_cmdline.h"
 #include "braille.h"
-#include "internal.h"
 
 int console_printk[4] = {
 	CONSOLE_LOGLEVEL_DEFAULT,	/* console_loglevel */
@@ -227,19 +227,7 @@ static int nr_ext_console_drivers;
 
 static int __down_trylock_console_sem(unsigned long ip)
 {
-	int lock_failed;
-	unsigned long flags;
-
-	/*
-	 * Here and in __up_console_sem() we need to be in safe mode,
-	 * because spindump/WARN/etc from under console ->lock will
-	 * deadlock in printk()->down_trylock_console_sem() otherwise.
-	 */
-	printk_safe_enter_irqsave(flags);
-	lock_failed = down_trylock(&console_sem);
-	printk_safe_exit_irqrestore(flags);
-
-	if (lock_failed)
+	if (down_trylock(&console_sem))
 		return 1;
 	mutex_acquire(&console_lock_dep_map, 0, 1, ip);
 	return 0;
@@ -248,13 +236,9 @@ static int __down_trylock_console_sem(un
 
 static void __up_console_sem(unsigned long ip)
 {
-	unsigned long flags;
-
 	mutex_release(&console_lock_dep_map, ip);
 
-	printk_safe_enter_irqsave(flags);
 	up(&console_sem);
-	printk_safe_exit_irqrestore(flags);
 }
 #define up_console_sem() __up_console_sem(_RET_IP_)
 
@@ -426,7 +410,7 @@ static struct printk_ringbuffer *prb = &
  */
 static bool __printk_percpu_data_ready __read_mostly;
 
-bool printk_percpu_data_ready(void)
+static bool printk_percpu_data_ready(void)
 {
 	return __printk_percpu_data_ready;
 }
@@ -1060,7 +1044,6 @@ void __init setup_log_buf(int early)
 	struct printk_record r;
 	size_t new_descs_size;
 	size_t new_infos_size;
-	unsigned long flags;
 	char *new_log_buf;
 	unsigned int free;
 	u64 seq;
@@ -1958,9 +1941,9 @@ static u16 printk_sprint(char *text, u16
 }
 
 __printf(4, 0)
-int vprintk_store(int facility, int level,
-		  const struct dev_printk_info *dev_info,
-		  const char *fmt, va_list args)
+static int vprintk_store(int facility, int level,
+			 const struct dev_printk_info *dev_info,
+			 const char *fmt, va_list args)
 {
 	const u32 caller_id = printk_caller_id();
 	struct prb_reserved_entry e;
@@ -2106,11 +2089,22 @@ asmlinkage int vprintk_emit(int facility
 }
 EXPORT_SYMBOL(vprintk_emit);
 
-int vprintk_default(const char *fmt, va_list args)
+__printf(1, 0)
+static int vprintk_default(const char *fmt, va_list args)
 {
 	return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
 }
-EXPORT_SYMBOL_GPL(vprintk_default);
+
+__printf(1, 0)
+static int vprintk_func(const char *fmt, va_list args)
+{
+#ifdef CONFIG_KGDB_KDB
+	/* Allow to pass printk() to kdb but avoid a recursion. */
+	if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0))
+		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
+#endif
+	return vprintk_default(fmt, args);
+}
 
 asmlinkage int vprintk(const char *fmt, va_list args)
 {
@@ -3073,18 +3067,10 @@ void wake_up_klogd(void)
 	preempt_enable();
 }
 
-void defer_console_output(void)
+__printf(1, 0)
+static int vprintk_deferred(const char *fmt, va_list args)
 {
-}
-
-int vprintk_deferred(const char *fmt, va_list args)
-{
-	int r;
-
-	r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args);
-	defer_console_output();
-
-	return r;
+	return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
 }
 
 int printk_deferred(const char *fmt, ...)
--- a/kernel/printk/printk_safe.c
+++ /dev/null
@@ -1,88 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-/*
- * printk_safe.c - Safe printk for printk-deadlock-prone contexts
- */
-
-#include <linux/preempt.h>
-#include <linux/spinlock.h>
-#include <linux/debug_locks.h>
-#include <linux/kdb.h>
-#include <linux/smp.h>
-#include <linux/cpumask.h>
-#include <linux/irq_work.h>
-#include <linux/printk.h>
-#include <linux/kprobes.h>
-
-#include "internal.h"
-
-static DEFINE_PER_CPU(int, printk_context);
-
-#ifdef CONFIG_PRINTK_NMI
-void noinstr printk_nmi_enter(void)
-{
-	this_cpu_add(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
-}
-
-void noinstr printk_nmi_exit(void)
-{
-	this_cpu_sub(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
-}
-
-/*
- * Marks a code that might produce many messages in NMI context
- * and the risk of losing them is more critical than eventual
- * reordering.
- */
-void printk_nmi_direct_enter(void)
-{
-	if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
-		this_cpu_or(printk_context, PRINTK_NMI_DIRECT_CONTEXT_MASK);
-}
-
-void printk_nmi_direct_exit(void)
-{
-	this_cpu_and(printk_context, ~PRINTK_NMI_DIRECT_CONTEXT_MASK);
-}
-
-#endif /* CONFIG_PRINTK_NMI */
-
-/* Can be preempted by NMI. */
-void __printk_safe_enter(void)
-{
-	this_cpu_inc(printk_context);
-}
-
-/* Can be preempted by NMI. */
-void __printk_safe_exit(void)
-{
-	this_cpu_dec(printk_context);
-}
-
-__printf(1, 0) int vprintk_func(const char *fmt, va_list args)
-{
-#ifdef CONFIG_KGDB_KDB
-	/* Allow to pass printk() to kdb but avoid a recursion. */
-	if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0))
-		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
-#endif
-
-	/*
-	 * Use the main logbuf even in NMI. But avoid calling console
-	 * drivers that might have their own locks.
-	 */
-	if (this_cpu_read(printk_context) &
-	    (PRINTK_NMI_DIRECT_CONTEXT_MASK |
-	     PRINTK_NMI_CONTEXT_MASK |
-	     PRINTK_SAFE_CONTEXT_MASK)) {
-		int len;
-
-		printk_safe_enter_irqsave(flags);
-		len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
-		printk_safe_exit_irqrestore(flags);
-		defer_console_output();
-		return len;
-	}
-
-	/* No obstacles. */
-	return vprintk_default(fmt, args);
-}
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -9325,7 +9325,6 @@ void ftrace_dump(enum ftrace_dump_mode o
 	tracing_off();
 
 	local_irq_save(flags);
-	printk_nmi_direct_enter();
 
 	/* Simulate the iterator */
 	trace_init_global_iter(&iter);
@@ -9405,7 +9404,6 @@ void ftrace_dump(enum ftrace_dump_mode o
 		atomic_dec(&per_cpu_ptr(iter.array_buffer->data, cpu)->disabled);
 	}
 	atomic_dec(&dump_running);
-	printk_nmi_direct_exit();
 	local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(ftrace_dump);