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Subject: Re: [GIT PULL] SLAB changes for v2.6.39-rc1
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>, Ingo Molnar <mingo@elte.hu>,
        torvalds@linux-foundation.org, akpm@linux-foundation.org,
        tj@kernel.org, npiggin@kernel.dk, rientjes@google.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
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Content-Type: text/plain; charset="UTF-8"
Date: Thu, 24 Mar 2011 19:20:53 +0100
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Le jeudi 24 mars 2011 à 13:15 -0500, Christoph Lameter a écrit :

> But then we would get the bug in kmem_cache_alloc() and not in the
> *_emu() function. So the _emu is executing but failing on Ingo's system
> but not on mine. Question is why.
> 
> For some reason the first reference to %gs:(%rsi) wont work right on his
> system:
> 
> From arch/x86/lib/cmpxchg16b_emu
> 
> #
> # Emulate 'cmpxchg16b %gs:(%rsi)' except we return the result in %al not
> # via the ZF.  Caller will access %al to get result.
> #
> # Note that this is only useful for a cpuops operation.  Meaning that we
> # do *not* have a fully atomic operation but just an operation that is
> # *atomic* on a single cpu (as provided by the this_cpu_xx class of
> # macros).
> #
> this_cpu_cmpxchg16b_emu:
>         pushf
>         cli
> 
>         cmpq %gs:(%rsi), %rax
>         jne not_same
>         cmpq %gs:8(%rsi), %rdx
>         jne not_same
> 
>         movq %rbx, %gs:(%rsi)
>         movq %rcx, %gs:8(%rsi)
> 
>         popf
>         mov $1, %al
>         ret
> 
>  not_same:
>         popf
>         xor %al,%al
>         ret
> 
> CFI_ENDPROC

Random guess

Masking interrupts, and accessing vmalloc() based memory for the first
time ?


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