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Date:	Thu, 19 Jun 2014 08:22:28 -0700
From:	Josh Triplett <>
To:	Bart Van Assche <>
Cc:	Arnd Bergmann <>,
	Andrew Morton <>,
	linux-kernel <>
Subject: Re: [PATCH] bug: Fix CONFIG_BUG=n BUG_ON()

On Thu, Jun 19, 2014 at 03:28:19PM +0200, 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().

No, this patch should not go in.  CONFIG_BUG=n exists for this exact
purpose; if you want BUG_ON to do something then use CONFIG_BUG=y with
BUGVERBOSE disabled instead.

Making BUG() stop the machine even with CONFIG_BUG=n eliminated a number
of compiler warnings about code that should be unreachable, and added
fairly little size to the kernel.  BUG_ON, on the other hand, occurs in
far more places, adds much more size if enabled, and tends to serve as
an assert of a condition; it makes perfect sense to allow compiling out
an assert, and compiling it out does not introduce any compiler

What problem are you trying to solve here?  With this change,
CONFIG_BUG=n and CONFIG_BUG=y would become effectively equivalent.


> --- 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))

Even if making this change, it should not take this form, which would
evaluate the conditional repeatedly.  See the form used with
CONFIG_BUG=y (without HAVE_ARCH_BUG_ON), defined earlier in the same

- Josh Triplett
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