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

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Message-ID: <BANLkTimvxOMuPJ0W0npo5i3gwFqdRw74Pw@mail.gmail.com>
Date:	Wed, 4 May 2011 14:19:31 -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 2:06 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> The problem is that cmpxchg *IS*NOT*AN*CMPXCHG*AT*ALL*. Not even on UP.

Btw, the really sad thing is that as far as I can tell, the
cmpxchg64_local() function that we define actually gets this *right*,
with a helper function that actually works (and disables interrupts)
and all the alternative_io() stuff to then use the right instruction
automatically if the CPU supports it, rather than making it a
hardcoded decision.

But we don't use it, because the "percpu_cmpxchg8b_double()" code
rolls its own inferior version, and has slightly different semantics
(ie the whole "return value success" thing).

So close, but yet so far.

                       Linus
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