[PATCH] asm-generic: add unlikely to default BUG_ON(x)

[PATCH] asm-generic: add unlikely to default BUG_ON(x)

[Denis Efremov]

Add unlikely to default BUG_ON(x) in !CONFIG_BUG. It makes
the define consistent with BUG_ON(x) in CONFIG_BUG.

Signed-off-by: Denis Efremov <efremov@linux.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: <linux-arch@vger.kernel.org>
---
 include/asm-generic/bug.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index aa6c093d9ce9..7357a3c942a0 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -185,7 +185,7 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
 #endif
 
 #ifndef HAVE_ARCH_BUG_ON
-#define BUG_ON(condition) do { if (condition) BUG(); } while (0)
+#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)
 #endif
 
 #ifndef HAVE_ARCH_WARN_ON
-- 
2.21.0

Re: [PATCH] asm-generic: add unlikely to default BUG_ON(x)

[Denis Efremov]

Maybe it will be better to move this define out of ifdef, i.e.:

#ifdef CONFIG_BUG
...
-#define BUG_ON()...
...
#else
...
-#define BUG_ON()...
...
#endif

+#define BUG_ON()...

I can prepare a patch if you think it worth it.

Thanks,
Denis

On 29.08.2019 00:09, Denis Efremov wrote:
> Add unlikely to default BUG_ON(x) in !CONFIG_BUG. It makes
> the define consistent with BUG_ON(x) in CONFIG_BUG.
> 
> Signed-off-by: Denis Efremov <efremov@linux.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: <linux-arch@vger.kernel.org>
> ---
>  include/asm-generic/bug.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
> index aa6c093d9ce9..7357a3c942a0 100644
> --- a/include/asm-generic/bug.h
> +++ b/include/asm-generic/bug.h
> @@ -185,7 +185,7 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
>  #endif
>  
>  #ifndef HAVE_ARCH_BUG_ON
> -#define BUG_ON(condition) do { if (condition) BUG(); } while (0)
> +#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)
>  #endif
>  
>  #ifndef HAVE_ARCH_WARN_ON
> 

Re: [PATCH] asm-generic: add unlikely to default BUG_ON(x)

[Arnd Bergmann]

On Wed, Aug 28, 2019 at 11:09 PM Denis Efremov <efremov@linux.com> wrote:
>
> Add unlikely to default BUG_ON(x) in !CONFIG_BUG. It makes
> the define consistent with BUG_ON(x) in CONFIG_BUG.
>
> Signed-off-by: Denis Efremov <efremov@linux.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: <linux-arch@vger.kernel.org>

This makes sense, I've applied it to the asm-generic tree for now.

Two concerns though:

- adding unlikely() can cause new (usually false-postive) compile time
  warnings to show up in random configurations, so we'll have to see what
  the build bots think

- Kees Cook has recently sent a series for asm/bug.h that was merged by
  Andrew Morton. If there are is a conflict with your patch, it may be better
  to merge both through the same tree, either linux-mm or asm-generic.

        Arnd

Re: [PATCH] asm-generic: add unlikely to default BUG_ON(x)

[Kees Cook]

On Fri, Aug 30, 2019 at 10:08:49PM +0200, Arnd Bergmann wrote:
> On Wed, Aug 28, 2019 at 11:09 PM Denis Efremov <efremov@linux.com> wrote:
> >
> > Add unlikely to default BUG_ON(x) in !CONFIG_BUG. It makes
> > the define consistent with BUG_ON(x) in CONFIG_BUG.
> >
> > Signed-off-by: Denis Efremov <efremov@linux.com>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: <linux-arch@vger.kernel.org>
> 
> This makes sense, I've applied it to the asm-generic tree for now.
> 
> Two concerns though:
> 
> - adding unlikely() can cause new (usually false-postive) compile time
>   warnings to show up in random configurations, so we'll have to see what
>   the build bots think
> 
> - Kees Cook has recently sent a series for asm/bug.h that was merged by
>   Andrew Morton. If there are is a conflict with your patch, it may be better
>   to merge both through the same tree, either linux-mm or asm-generic.

FWIW, this patch looks sensible to me. :)

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook