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Date: Wed, 4 May 2011 16:07:42 +0200
From: Tejun Heo <tj@kernel.org>
To: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@elte.hu>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jens Axboe <axboe@kernel.dk>,
        Andrew Morton <akpm@linux-foundation.org>, werner <w.landgraf@ru.ru>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [block IO crash] Re: 2.6.39-rc5-git2 boot crashs
Message-ID: <20110504140742.GB17294@htj.dyndns.org>
References: <web-516990066@zbackend1.aha.ru>
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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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