linux-kernel - Re: [PATCH] ARM: BUG() dies silently

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Message-ID: <CAH+eYFBSiL44CMOpgED+TAOTUH_dQMaKKu=hC3ynG0Y2nQ8ekw@mail.gmail.com>
Date:	Sat, 17 Sep 2011 11:37:26 +0530
From:	Rabin Vincent <rabin@....in>
To:	Omar Ramirez Luna <omar.ramirez@...com>
Cc:	Russell King <linux@....linux.org.uk>,
	lak <linux-arm-kernel@...ts.infradead.org>,
	lk <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: BUG() dies silently

On Fri, Apr 1, 2011 at 01:45, Omar Ramirez Luna <omar.ramirez@...com> wrote:
> There are some cases where the code generated for BUG() results
> into an infinite while loop without causing a null dereference,
> this ends on a kernel being stuck on a loop and the user without
> a clue of what happened.
>
> E.g.: lib/scatterlist.c : __sg_alloc_table
>
>        BUG_ON(nents > max_ents);
>  438:   9a000000        bls     440 <__sg_alloc_table+0x20>
>  43c:   eafffffe        b       43c <__sg_alloc_table+0x1c>
>
> Adding volatile makes the compiler to avoid optimizations on this
> code, which makes the panic to occur:
>
>        BUG_ON(nents > max_ents);
>  438:   9a000002        bls     448 <__sg_alloc_table+0x28>
>  43c:   e3a03000        mov     r3, #0
>  440:   e5833000        str     r3, [r3]
>  444:   eafffffc        b       43c <__sg_alloc_table+0x1c>
>
> Seen with gnu/linux cs arm-2010q1-202 and arm2010.09-50.
>
> Signed-off-by: Omar Ramirez Luna <omar.ramirez@...com>

If the "Use generic BUG() handler" patch is only scheduled for the next
merge window and not for 3.1, can this patch be merged instead for 3.1
and -stable?  This problem is easily seen with GCC 4.6.
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