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

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Message-ID: <20110504140742.GB17294@htj.dyndns.org>
Date:	Wed, 4 May 2011 16:07:42 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Pekka Enberg <penberg@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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

Hello, Christoph.

On Wed, May 04, 2011 at 09:04:19AM -0500, Christoph Lameter wrote:
> The above should not happen. If a kernel config indicates that there is no
> cmpxchg16b/cmpxchg8b available then we need to not compile the path that
> uses cmpxchg8b/cmpxchg16b. Guess we need CMPXCHG_DOUBLE_LOCAL or so.

But regardless of that, if the code requires irq safety it should be
using irqsafe_* operations.  CMPXCHG_LOCAL is an optimization hint and
doesn't necessarily imply stronger synchronization guarantees.  In
addition, there's no downside to using irqsafe_* variant when CPU
actually supports cmpxchg[_double].  So, let's first fix that and
think about CMPXCHG[_DOUBLE]_LOCAL or whatnot later.

Thank you.

-- 
tejun
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