linux-kernel - Re: [GIT PULL] SLAB changes for v2.6.39-rc1

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Message-ID: <AANLkTimMcP-GikCCndQppNBsS7y=4beesZ4PaD6yh5y5@mail.gmail.com>
Date:	Thu, 24 Mar 2011 19:56:35 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Ingo Molnar <mingo@...e.hu>, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, tj@...nel.org, npiggin@...nel.dk,
	rientjes@...gle.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [GIT PULL] SLAB changes for v2.6.39-rc1

On Thu, 24 Mar 2011, Ingo Molnar wrote:
>> > How does alternative_io() work? Does it require
>> > alternative_instructions() to be executed. If so, the fallback code
>> > won't be active when we enter kmem_cache_init(). Is there any reason
>> > check_bugs() is called so late during boot? Can we do something like
>> > the totally untested attached patch?
>>
>> Does the config i sent you boot on your box? I think the bug is pretty generic
>> and should trigger on any box.

On Thu, Mar 24, 2011 at 7:43 PM, Christoph Lameter <cl@...ux.com> wrote:
> The bug should only trigger on old AMD64 boxes that do not support
> cmpxchg16b.

Yup. Ingo is it possible to see /proc/cpuinfo of one of the affected
boxes? I'll try your config but I'm pretty sure the problem doesn't
trigger here. Like I said, I think the problem is that alternative
instructions are not patched early enough for cmpxchg16b emulation to
work for kmem_cache_init(). I tried my check_bugs() patch but it hangs
during boot. I'll see if I can cook up a patch that does
alternative_instructions() before kmem_cache_init() because I think
those *should* be available during boot too.

                        Pekka
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