Re: [PATCH] Support resetting WARN*_ONCE

Michael Ellerman
2017-10-18T05:35:17Z

Andi Kleen <andi@firstfloor.org> writes:

> From: Andi Kleen <ak@linux.intel.com>
>
> 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.

That won't work for arches that do the ONCE logic with a flag will it?
ie. arm64, parisc, powerpc, s390, sh, x86.

They use the version of WARN_ON_ONCE at line ~64 of bug.h

#define __WARN_ONCE_TAINT(taint) __WARN_FLAGS(BUGFLAG_ONCE|BUGFLAG_TAINT(taint))

#define WARN_ON_ONCE(condition) ({ \
int __ret_warn_on = !!(condition); \
if (unlikely(__ret_warn_on)) \
__WARN_ONCE_TAINT(TAINT_WARN); \
unlikely(__ret_warn_on); \
})

cheers

> diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
> index 87191357d303..68c2f08b7914 100644
> --- a/include/asm-generic/bug.h
> +++ b/include/asm-generic/bug.h
> @@ -129,7 +129,7 @@ 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)) { \
> @@ -141,7 +141,7 @@ 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)) { \
> @@ -152,7 +152,7 @@ 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)) { \