linux-kernel - Re: [block IO crash] Re: 2.6.39-rc5-git2 boot crashs

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Message-ID: <BANLkTik7AHGr7+BG8nE16j-ayctD0LOH=w@mail.gmail.com>
Date:	Wed, 4 May 2011 14:06:21 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Pekka Enberg <penberg@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Jens Axboe <axboe@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	werner <w.landgraf@...ru>, "H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [block IO crash] Re: 2.6.39-rc5-git2 boot crashs

On Wed, May 4, 2011 at 1:04 PM, Christoph Lameter <cl@...ux.com> wrote:
>
> Maybe I should have pushed the cmpxchg_double() before the
> this_cpu_cmpxchg to avoid these misunderstandings

Christoph, the only mis-understanding is yours.

I understand perfectly that the percpu cmpxchg isn't SMP-atomic. We
all know that.

The problem is that cmpxchg *IS*NOT*AN*CMPXCHG*AT*ALL*. Not even on UP.

It's something totally different.

                   Linus
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