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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>
This commit is contained in:
John Ogness 2019-02-12 15:29:49 +01:00 committed by Alibek Omarov
parent 5c57b182f2
commit acc072bdd0
12 changed files with 7 additions and 498 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/powerpc/kernel/traps.c
View File

@ -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();

5
arch/powerpc/kernel/watchdog.c
View File

@ -181,11 +181,6 @@ 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();

2
include/linux/hardirq.h
View File

@ -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)

22
include/linux/printk.h
View File

@ -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,
@ -202,8 +190,6 @@ __printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...);
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_flush(void);
extern void printk_safe_flush_on_panic(void);
#else
static inline __printf(1, 0)
int vprintk(const char *s, va_list args)
@ -267,14 +253,6 @@ static inline void show_regs_print_info(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
extern int kptr_restrict;

1
kernel/kexec_core.c
View File

@ -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);
/*

3
kernel/panic.c
View File

@ -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);
/*

1
kernel/printk/Makefile
View File

@ -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

35
kernel/printk/internal.h
View File

@ -20,35 +20,6 @@ int vprintk_store(int facility, int level,
__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);
void printk_safe_init(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);
@ -61,12 +32,10 @@ __printf(1, 0) int vprintk_func(const char *fmt, va_list args) { return 0; }
* 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()
static inline void printk_safe_init(void) { }
static inline bool printk_percpu_data_ready(void) { return false; }
#endif /* CONFIG_PRINTK */

13
kernel/printk/printk.c
View File

@ -1764,13 +1764,6 @@ static bool cont_add(u32 caller_id, int facility, int level,
}
#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) +
@ -1839,6 +1832,11 @@ asmlinkage int vprintk_emit(int facility, int level,
}
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);
@ -3255,5 +3253,4 @@ void kmsg_dump_rewind(struct kmsg_dumper *dumper)
logbuf_unlock_irqrestore(flags);
}
EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
#endif

414
kernel/printk/printk_safe.c
View File

@ -1,414 +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.
*/
#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);
static DEFINE_RAW_SPINLOCK(safe_read_lock);
#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_percpu_data_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)
{
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(&safe_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(&safe_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);
}
if (raw_spin_is_locked(&safe_read_lock)) {
if (num_online_cpus() > 1)
return;
debug_locks_off();
raw_spin_lock_init(&safe_read_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
}
/* Flush pending messages that did not have scheduled IRQ works. */
printk_safe_flush();
}

2
kernel/trace/trace.c
View File

@ -8959,7 +8959,6 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
tracing_off();
local_irq_save(flags);
printk_nmi_direct_enter();
/* Simulate the iterator */
trace_init_global_iter(&iter);
@ -9036,7 +9035,6 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
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);

6
lib/nmi_backtrace.c
View File

@ -75,12 +75,6 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
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();
}