path: root/patches/0011-printk_safe-remove-printk-safe-code.patch

From: John Ogness <john.ogness@linutronix.de>
Date: Tue, 12 Feb 2019 15:29:49 +0100
Subject: [PATCH 11/25] printk_safe: remove printk safe code

vprintk variants are now NMI-safe so there is no longer a need for
the "safe" calls.

NOTE: This also removes printk flushing functionality.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 arch/powerpc/kernel/traps.c    |    1 
 arch/powerpc/kernel/watchdog.c |    5 
 include/linux/hardirq.h        |    2 
 include/linux/printk.h         |   27 --
 init/main.c                    |    1 
 kernel/kexec_core.c            |    1 
 kernel/panic.c                 |    3 
 kernel/printk/Makefile         |    1 
 kernel/printk/internal.h       |   30 --
 kernel/printk/printk.c         |   13 -
 kernel/printk/printk_safe.c    |  415 -----------------------------------------
 kernel/trace/trace.c           |    2 
 lib/nmi_backtrace.c            |    6 
 13 files changed, 7 insertions(+), 500 deletions(-)
 delete mode 100644 kernel/printk/printk_safe.c

--- 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();
--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -181,11 +181,6 @@ static void watchdog_smp_panic(int cpu,
 
 	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();
 
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -68,7 +68,6 @@ extern void irq_exit(void);
 #define nmi_enter()						\
 	do {							\
 		arch_nmi_enter();				\
-		printk_nmi_enter();				\
 		lockdep_off();					\
 		ftrace_nmi_enter();				\
 		BUG_ON(in_nmi());				\
@@ -85,7 +84,6 @@ extern void irq_exit(void);
 		preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET);	\
 		ftrace_nmi_exit();				\
 		lockdep_on();					\
-		printk_nmi_exit();				\
 		arch_nmi_exit();				\
 	} while (0)
 
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -146,18 +146,6 @@ 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 */
-
 #ifdef CONFIG_PRINTK
 asmlinkage __printf(5, 0)
 int vprintk_emit(int facility, int level,
@@ -202,9 +190,6 @@ void __init setup_log_buf(int early);
 void dump_stack_print_info(const char *log_lvl);
 void show_regs_print_info(const char *log_lvl);
 extern asmlinkage void dump_stack(void) __cold;
-extern void printk_safe_init(void);
-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)
@@ -268,18 +253,6 @@ static inline void show_regs_print_info(
 static inline void dump_stack(void)
 {
 }
-
-static inline void printk_safe_init(void)
-{
-}
-
-static inline void printk_safe_flush(void)
-{
-}
-
-static inline void printk_safe_flush_on_panic(void)
-{
-}
 #endif
 
 extern int kptr_restrict;
--- a/init/main.c
+++ b/init/main.c
@@ -694,7 +694,6 @@ asmlinkage __visible void __init start_k
 	boot_init_stack_canary();
 
 	time_init();
-	printk_safe_init();
 	perf_event_init();
 	profile_init();
 	call_function_init();
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -972,7 +972,6 @@ void crash_kexec(struct pt_regs *regs)
 	old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu);
 	if (old_cpu == PANIC_CPU_INVALID) {
 		/* This is the 1st CPU which comes here, so go ahead. */
-		printk_safe_flush_on_panic();
 		__crash_kexec(regs);
 
 		/*
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -237,7 +237,6 @@ void panic(const char *fmt, ...)
 	 * Bypass the panic_cpu check and call __crash_kexec directly.
 	 */
 	if (!_crash_kexec_post_notifiers) {
-		printk_safe_flush_on_panic();
 		__crash_kexec(NULL);
 
 		/*
@@ -261,8 +260,6 @@ void panic(const char *fmt, ...)
 	 */
 	atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
 
-	/* Call flush even twice. It tries harder with a single online CPU */
-	printk_safe_flush_on_panic();
 	kmsg_dump(KMSG_DUMP_PANIC);
 
 	/*
--- a/kernel/printk/Makefile
+++ b/kernel/printk/Makefile
@@ -1,4 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-y	= printk.o
-obj-$(CONFIG_PRINTK)	+= printk_safe.o
 obj-$(CONFIG_A11Y_BRAILLE_CONSOLE)	+= braille.o
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -20,32 +20,6 @@ int vprintk_store(int facility, int leve
 __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);
-
-#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);
 
@@ -58,10 +32,10 @@ void defer_console_output(void);
  * semaphore and some of console functions (console_unlock()/etc.), so
  * printk-safe must preserve the existing local IRQ guarantees.
  */
+#endif /* CONFIG_PRINTK */
+
 #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()
-
-#endif /* CONFIG_PRINTK */
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1736,13 +1736,6 @@ static bool cont_add(u32 caller_id, int
 }
 #endif /* 0 */
 
-int vprintk_store(int facility, int level,
-		  const char *dict, size_t dictlen,
-		  const char *fmt, va_list args)
-{
-	return vprintk_emit(facility, level, dict, dictlen, fmt, args);
-}
-
 /* ring buffer used as memory allocator for temporary sprint buffers */
 DECLARE_STATIC_PRINTKRB(sprint_rb,
 			ilog2(PRINTK_RECORD_MAX + sizeof(struct prb_entry) +
@@ -1811,6 +1804,11 @@ asmlinkage int vprintk_emit(int facility
 }
 EXPORT_SYMBOL(vprintk_emit);
 
+__printf(1, 0) int vprintk_func(const char *fmt, va_list args)
+{
+	return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
+}
+
 asmlinkage int vprintk(const char *fmt, va_list args)
 {
 	return vprintk_func(fmt, args);
@@ -3211,5 +3209,4 @@ void kmsg_dump_rewind(struct kmsg_dumper
 	logbuf_unlock_irqrestore(flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
-
 #endif
--- a/kernel/printk/printk_safe.c
+++ /dev/null
@@ -1,415 +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/smp.h>
-#include <linux/cpumask.h>
-#include <linux/irq_work.h>
-#include <linux/printk.h>
-
-#include "internal.h"
-
-/*
- * printk() could not take logbuf_lock in NMI context. Instead,
- * it uses an alternative implementation that temporary stores
- * the strings into a per-CPU buffer. The content of the buffer
- * is later flushed into the main ring buffer via IRQ work.
- *
- * The alternative implementation is chosen transparently
- * by examinig current printk() context mask stored in @printk_context
- * per-CPU variable.
- *
- * The implementation allows to flush the strings also from another CPU.
- * There are situations when we want to make sure that all buffers
- * were handled or when IRQs are blocked.
- */
-static int printk_safe_irq_ready __read_mostly;
-
-#define SAFE_LOG_BUF_LEN ((1 << CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT) -	\
-				sizeof(atomic_t) -			\
-				sizeof(atomic_t) -			\
-				sizeof(struct irq_work))
-
-struct printk_safe_seq_buf {
-	atomic_t		len;	/* length of written data */
-	atomic_t		message_lost;
-	struct irq_work		work;	/* IRQ work that flushes the buffer */
-	unsigned char		buffer[SAFE_LOG_BUF_LEN];
-};
-
-static DEFINE_PER_CPU(struct printk_safe_seq_buf, safe_print_seq);
-static DEFINE_PER_CPU(int, printk_context);
-
-#ifdef CONFIG_PRINTK_NMI
-static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq);
-#endif
-
-/* Get flushed in a more safe context. */
-static void queue_flush_work(struct printk_safe_seq_buf *s)
-{
-	if (printk_safe_irq_ready)
-		irq_work_queue(&s->work);
-}
-
-/*
- * Add a message to per-CPU context-dependent buffer. NMI and printk-safe
- * have dedicated buffers, because otherwise printk-safe preempted by
- * NMI-printk would have overwritten the NMI messages.
- *
- * The messages are flushed from irq work (or from panic()), possibly,
- * from other CPU, concurrently with printk_safe_log_store(). Should this
- * happen, printk_safe_log_store() will notice the buffer->len mismatch
- * and repeat the write.
- */
-static __printf(2, 0) int printk_safe_log_store(struct printk_safe_seq_buf *s,
-						const char *fmt, va_list args)
-{
-	int add;
-	size_t len;
-	va_list ap;
-
-again:
-	len = atomic_read(&s->len);
-
-	/* The trailing '\0' is not counted into len. */
-	if (len >= sizeof(s->buffer) - 1) {
-		atomic_inc(&s->message_lost);
-		queue_flush_work(s);
-		return 0;
-	}
-
-	/*
-	 * Make sure that all old data have been read before the buffer
-	 * was reset. This is not needed when we just append data.
-	 */
-	if (!len)
-		smp_rmb();
-
-	va_copy(ap, args);
-	add = vscnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, ap);
-	va_end(ap);
-	if (!add)
-		return 0;
-
-	/*
-	 * Do it once again if the buffer has been flushed in the meantime.
-	 * Note that atomic_cmpxchg() is an implicit memory barrier that
-	 * makes sure that the data were written before updating s->len.
-	 */
-	if (atomic_cmpxchg(&s->len, len, len + add) != len)
-		goto again;
-
-	queue_flush_work(s);
-	return add;
-}
-
-static inline void printk_safe_flush_line(const char *text, int len)
-{
-	/*
-	 * Avoid any console drivers calls from here, because we may be
-	 * in NMI or printk_safe context (when in panic). The messages
-	 * must go only into the ring buffer at this stage.  Consoles will
-	 * get explicitly called later when a crashdump is not generated.
-	 */
-	printk_deferred("%.*s", len, text);
-}
-
-/* printk part of the temporary buffer line by line */
-static int printk_safe_flush_buffer(const char *start, size_t len)
-{
-	const char *c, *end;
-	bool header;
-
-	c = start;
-	end = start + len;
-	header = true;
-
-	/* Print line by line. */
-	while (c < end) {
-		if (*c == '\n') {
-			printk_safe_flush_line(start, c - start + 1);
-			start = ++c;
-			header = true;
-			continue;
-		}
-
-		/* Handle continuous lines or missing new line. */
-		if ((c + 1 < end) && printk_get_level(c)) {
-			if (header) {
-				c = printk_skip_level(c);
-				continue;
-			}
-
-			printk_safe_flush_line(start, c - start);
-			start = c++;
-			header = true;
-			continue;
-		}
-
-		header = false;
-		c++;
-	}
-
-	/* Check if there was a partial line. Ignore pure header. */
-	if (start < end && !header) {
-		static const char newline[] = KERN_CONT "\n";
-
-		printk_safe_flush_line(start, end - start);
-		printk_safe_flush_line(newline, strlen(newline));
-	}
-
-	return len;
-}
-
-static void report_message_lost(struct printk_safe_seq_buf *s)
-{
-	int lost = atomic_xchg(&s->message_lost, 0);
-
-	if (lost)
-		printk_deferred("Lost %d message(s)!\n", lost);
-}
-
-/*
- * Flush data from the associated per-CPU buffer. The function
- * can be called either via IRQ work or independently.
- */
-static void __printk_safe_flush(struct irq_work *work)
-{
-	static raw_spinlock_t read_lock =
-		__RAW_SPIN_LOCK_INITIALIZER(read_lock);
-	struct printk_safe_seq_buf *s =
-		container_of(work, struct printk_safe_seq_buf, work);
-	unsigned long flags;
-	size_t len;
-	int i;
-
-	/*
-	 * The lock has two functions. First, one reader has to flush all
-	 * available message to make the lockless synchronization with
-	 * writers easier. Second, we do not want to mix messages from
-	 * different CPUs. This is especially important when printing
-	 * a backtrace.
-	 */
-	raw_spin_lock_irqsave(&read_lock, flags);
-
-	i = 0;
-more:
-	len = atomic_read(&s->len);
-
-	/*
-	 * This is just a paranoid check that nobody has manipulated
-	 * the buffer an unexpected way. If we printed something then
-	 * @len must only increase. Also it should never overflow the
-	 * buffer size.
-	 */
-	if ((i && i >= len) || len > sizeof(s->buffer)) {
-		const char *msg = "printk_safe_flush: internal error\n";
-
-		printk_safe_flush_line(msg, strlen(msg));
-		len = 0;
-	}
-
-	if (!len)
-		goto out; /* Someone else has already flushed the buffer. */
-
-	/* Make sure that data has been written up to the @len */
-	smp_rmb();
-	i += printk_safe_flush_buffer(s->buffer + i, len - i);
-
-	/*
-	 * Check that nothing has got added in the meantime and truncate
-	 * the buffer. Note that atomic_cmpxchg() is an implicit memory
-	 * barrier that makes sure that the data were copied before
-	 * updating s->len.
-	 */
-	if (atomic_cmpxchg(&s->len, len, 0) != len)
-		goto more;
-
-out:
-	report_message_lost(s);
-	raw_spin_unlock_irqrestore(&read_lock, flags);
-}
-
-/**
- * printk_safe_flush - flush all per-cpu nmi buffers.
- *
- * The buffers are flushed automatically via IRQ work. This function
- * is useful only when someone wants to be sure that all buffers have
- * been flushed at some point.
- */
-void printk_safe_flush(void)
-{
-	int cpu;
-
-	for_each_possible_cpu(cpu) {
-#ifdef CONFIG_PRINTK_NMI
-		__printk_safe_flush(&per_cpu(nmi_print_seq, cpu).work);
-#endif
-		__printk_safe_flush(&per_cpu(safe_print_seq, cpu).work);
-	}
-}
-
-/**
- * printk_safe_flush_on_panic - flush all per-cpu nmi buffers when the system
- *	goes down.
- *
- * Similar to printk_safe_flush() but it can be called even in NMI context when
- * the system goes down. It does the best effort to get NMI messages into
- * the main ring buffer.
- *
- * Note that it could try harder when there is only one CPU online.
- */
-void printk_safe_flush_on_panic(void)
-{
-	/*
-	 * Make sure that we could access the main ring buffer.
-	 * Do not risk a double release when more CPUs are up.
-	 */
-	if (raw_spin_is_locked(&logbuf_lock)) {
-		if (num_online_cpus() > 1)
-			return;
-
-		debug_locks_off();
-		raw_spin_lock_init(&logbuf_lock);
-	}
-
-	printk_safe_flush();
-}
-
-#ifdef CONFIG_PRINTK_NMI
-/*
- * Safe printk() for NMI context. It uses a per-CPU buffer to
- * store the message. NMIs are not nested, so there is always only
- * one writer running. But the buffer might get flushed from another
- * CPU, so we need to be careful.
- */
-static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
-{
-	struct printk_safe_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
-
-	return printk_safe_log_store(s, fmt, args);
-}
-
-void notrace printk_nmi_enter(void)
-{
-	this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK);
-}
-
-void notrace printk_nmi_exit(void)
-{
-	this_cpu_and(printk_context, ~PRINTK_NMI_CONTEXT_MASK);
-}
-
-/*
- * Marks a code that might produce many messages in NMI context
- * and the risk of losing them is more critical than eventual
- * reordering.
- *
- * It has effect only when called in NMI context. Then printk()
- * will try to store the messages into the main logbuf directly
- * and use the per-CPU buffers only as a fallback when the lock
- * is not available.
- */
-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);
-}
-
-#else
-
-static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
-{
-	return 0;
-}
-
-#endif /* CONFIG_PRINTK_NMI */
-
-/*
- * Lock-less printk(), to avoid deadlocks should the printk() recurse
- * into itself. It uses a per-CPU buffer to store the message, just like
- * NMI.
- */
-static __printf(1, 0) int vprintk_safe(const char *fmt, va_list args)
-{
-	struct printk_safe_seq_buf *s = this_cpu_ptr(&safe_print_seq);
-
-	return printk_safe_log_store(s, fmt, args);
-}
-
-/* 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)
-{
-	/*
-	 * Try to 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) &&
-	    raw_spin_trylock(&logbuf_lock)) {
-		int len;
-
-		len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
-		raw_spin_unlock(&logbuf_lock);
-		defer_console_output();
-		return len;
-	}
-
-	/* Use extra buffer in NMI when logbuf_lock is taken or in safe mode. */
-	if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
-		return vprintk_nmi(fmt, args);
-
-	/* Use extra buffer to prevent a recursion deadlock in safe mode. */
-	if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK)
-		return vprintk_safe(fmt, args);
-
-	/* No obstacles. */
-	return vprintk_default(fmt, args);
-}
-
-void __init printk_safe_init(void)
-{
-	int cpu;
-
-	for_each_possible_cpu(cpu) {
-		struct printk_safe_seq_buf *s;
-
-		s = &per_cpu(safe_print_seq, cpu);
-		init_irq_work(&s->work, __printk_safe_flush);
-
-#ifdef CONFIG_PRINTK_NMI
-		s = &per_cpu(nmi_print_seq, cpu);
-		init_irq_work(&s->work, __printk_safe_flush);
-#endif
-	}
-
-	/*
-	 * In the highly unlikely event that a NMI were to trigger at
-	 * this moment. Make sure IRQ work is set up before this
-	 * variable is set.
-	 */
-	barrier();
-	printk_safe_irq_ready = 1;
-
-	/* Flush pending messages that did not have scheduled IRQ works. */
-	printk_safe_flush();
-}
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8927,7 +8927,6 @@ 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);
@@ -9004,7 +9003,6 @@ void ftrace_dump(enum ftrace_dump_mode o
 		atomic_dec(&per_cpu_ptr(iter.trace_buffer->data, cpu)->disabled);
 	}
 	atomic_dec(&dump_running);
-	printk_nmi_direct_exit();
 	local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(ftrace_dump);
--- a/lib/nmi_backtrace.c
+++ b/lib/nmi_backtrace.c
@@ -75,12 +75,6 @@ void nmi_trigger_cpumask_backtrace(const
 		touch_softlockup_watchdog();
 	}
 
-	/*
-	 * Force flush any remote buffers that might be stuck in IRQ context
-	 * and therefore could not run their irq_work.
-	 */
-	printk_safe_flush();
-
 	clear_bit_unlock(0, &backtrace_flag);
 	put_cpu();
 }