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Message-ID: <20111123071349.GA1671@x4.trippels.de>
Date: Wed, 23 Nov 2011 08:13:49 +0100
From: Markus Trippelsdorf <markus@...ppelsdorf.de>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: Christoph Lameter <cl@...ux.com>,
Christian Kujau <lists@...dbynature.de>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
"Alex,Shi" <alex.shi@...el.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
Pekka Enberg <penberg@...nel.org>,
Matt Mackall <mpm@...enic.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
Tejun Heo <tj@...nel.org>
Subject: Re: WARNING: at mm/slub.c:3357, kernel BUG at mm/slub.c:3413
On 2011.11.22 at 09:27 +0100, Eric Dumazet wrote:
> Le mardi 22 novembre 2011 à 08:48 +0100, Eric Dumazet a écrit :
>
> > For x86, I wonder if our !X86_FEATURE_CX16 support is correct on SMP
> > machines.
> >
>
>
> By the way, I wonder why we still emit this_cpu_cmpxchg16b_emu() code
> and calls when compiling a kernel for a cpu implementing cmpxchg16b
>
> (CONFIG_MCORE2=y)
Yeah, it's strange (CONFIG_MK8):
ffffffff811058b0 <__kmalloc>:
...
ffffffff8110594f: 48 8d 4a 04 lea 0x4(%rdx),%rcx
ffffffff81105953: 49 8b 1c 04 mov (%r12,%rax,1),%rbx
ffffffff81105957: 4c 89 e0 mov %r12,%rax
ffffffff8110595a: e8 11 70 10 00 callq ffffffff8120c970 <this_cpu_cmpxchg16b_emu>
ffffffff8110595f: 66 66 90 data32 xchg %ax,%ax
ffffffff81105962: 84 c0 test %al,%al
ffffffff81105964: 74 c6 je ffffffff8110592c <__kmalloc+0x7c>
...
There is a comment in arch/x86/include/asm/percpu.h:
* Pretty complex macro to generate cmpxchg16 instruction. The instruction
* is not supported on early AMD64 processors so we must be able to emulate
* it in software. The address used in the cmpxchg16 instruction must be
* aligned to a 16 byte boundary.
--
Markus
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