linux-kernel - Re: [PATCH] bug: Fix CONFIG_BUG=n BUG

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Message-ID: <5061693.b4BPIj9quA@wuerfel>
Date:	Thu, 19 Jun 2014 19:00:14 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Bart Van Assche <bvanassche@....org>
Cc:	Josh Triplett <josh@...htriplett.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bug: Fix CONFIG_BUG=n BUG_ON()

On Thursday 19 June 2014 15:28:19 Bart Van Assche wrote:
> Patch "bug: Make BUG() always stop the machine" changed the
> behavior of BUG() with CONFIG_BUG=n from a no-op into an infinite
> loop. Modify the definition of BUG_ON() accordingly such that the
> behavior of BUG_ON(1) is identical to that of BUG().
> 
> Signed-off-by: Bart Van Assche <bvanassche@....org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Josh Triplett <josh@...htriplett.org>
> Cc: Andrew Morton <akpm@...ux-foundation.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 630dd23..f3241cd 100644
> --- a/include/asm-generic/bug.h
> +++ b/include/asm-generic/bug.h
> @@ -142,7 +142,7 @@ extern void warn_slowpath_null(const char *file, const int line);
>  #endif
>  
>  #ifndef HAVE_ARCH_BUG_ON
> -#define BUG_ON(condition) do { if (condition) ; } while (0)
> +#define BUG_ON(condition) do { } while (unlikely(condition))
>  #endif
>  
>  #ifndef HAVE_ARCH_WARN_ON
> 

How about making it 

	do { if (condition) BUG(); } while (0)

That way it can be optimized for architectures that have their own
BUG but not BUG_ON.

	Arnd
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