Re: [PATCH] ARM: BUG() dies silently
From: Rabin Vincent
Date: Sat Sep 17 2011 - 02:08:10 EST
On Fri, Apr 1, 2011 at 01:45, Omar Ramirez Luna <omar.ramirez@xxxxxx> 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@xxxxxx>
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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