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kernel debug: support resetting WARN*_ONCE 

I like _ONCE warnings because it's guaranteed that they don't flood the
log.

During testing I find it useful to reset the state of the once warnings,
so that I can rerun tests and see if they trigger again, or can
guarantee that a test run always hits the same warnings.

This patch adds a debugfs interface to reset all the _ONCE warnings so
that they appear again:

  echo 1 > /sys/kernel/debug/clear_warn_once

This is implemented by putting all the warning booleans into a special
section, and clearing it.

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20171017221455.6740-1-andi@firstfloor.org
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Tested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andi Kleen 2017-11-17 15:27:03 -08:00 committed by Linus Torvalds
parent fb6cc4ac15
commit b1fca27d38
5 changed files with 42 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
Documentation/clearing-warn-once.txt Normal file
View File

@ -0,0 +1,7 @@
WARN_ONCE / WARN_ON_ONCE only print a warning once.
echo 1 > /sys/kernel/debug/clear_warn_once
clears the state and allows the warnings to print once again.
This can be useful after test suite runs to reproduce problems.

6
include/asm-generic/bug.h
View File

@ -130,7 +130,7 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
#ifndef WARN_ON_ONCE
#define WARN_ON_ONCE(condition) ({ \
static bool __section(.data.unlikely) __warned; \
static bool __section(.data.once) __warned; \
int __ret_warn_once = !!(condition); \
\
if (unlikely(__ret_warn_once && !__warned)) { \
@ -142,7 +142,7 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
#endif
#define WARN_ONCE(condition, format...) ({ \
static bool __section(.data.unlikely) __warned; \
static bool __section(.data.once) __warned; \
int __ret_warn_once = !!(condition); \
\
if (unlikely(__ret_warn_once && !__warned)) { \
@ -153,7 +153,7 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
})
#define WARN_TAINT_ONCE(condition, taint, format...) ({ \
static bool __section(.data.unlikely) __warned; \
static bool __section(.data.once) __warned; \
int __ret_warn_once = !!(condition); \
\
if (unlikely(__ret_warn_once && !__warned)) { \

1
include/asm-generic/sections.h
View File

@ -44,6 +44,7 @@ extern char __entry_text_start[], __entry_text_end[];
extern char __start_rodata[], __end_rodata[];
extern char __irqentry_text_start[], __irqentry_text_end[];
extern char __softirqentry_text_start[], __softirqentry_text_end[];
extern char __start_once[], __end_once[];
/* Start and end of .ctors section - used for constructor calls. */
extern char __ctors_start[], __ctors_end[];

3
include/asm-generic/vmlinux.lds.h
View File

@ -223,6 +223,9 @@
MEM_KEEP(init.data) \
MEM_KEEP(exit.data) \
*(.data.unlikely) \
VMLINUX_SYMBOL(__start_once) = .; \
*(.data.once) \
VMLINUX_SYMBOL(__end_once) = .; \
STRUCT_ALIGN(); \
*(__tracepoints) \
/* implement dynamic printk debug */ \

28
kernel/panic.c
View File

@ -27,6 +27,8 @@
#include <linux/console.h>
#include <linux/bug.h>
#include <linux/ratelimit.h>
#include <linux/debugfs.h>
#include <asm/sections.h>
#define PANIC_TIMER_STEP 100
#define PANIC_BLINK_SPD 18
@ -587,6 +589,32 @@ void warn_slowpath_null(const char *file, int line)
EXPORT_SYMBOL(warn_slowpath_null);
#endif
#ifdef CONFIG_BUG
/* Support resetting WARN*_ONCE state */
static int clear_warn_once_set(void *data, u64 val)
{
memset(__start_once, 0, __end_once - __start_once);
return 0;
}
DEFINE_SIMPLE_ATTRIBUTE(clear_warn_once_fops,
NULL,
clear_warn_once_set,
"%lld\n");
static __init int register_warn_debugfs(void)
{
/* Don't care about failure */
debugfs_create_file("clear_warn_once", 0644, NULL,
NULL, &clear_warn_once_fops);
return 0;
}
device_initcall(register_warn_debugfs);
#endif
#ifdef CONFIG_CC_STACKPROTECTOR
/*