linux-kernel - Re: [PATCH] MTRR: Fix race causing set

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Message-ID: <46841175.8070901@redhat.com>
Date:	Thu, 28 Jun 2007 15:52:21 -0400
From:	Chuck Ebbert <cebbert@...hat.com>
To:	Andi Kleen <ak@...e.de>
CC:	Loic Prylli <loic@...i.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MTRR: Fix race causing set_mtrr to go into infinite loop

On 06/25/2007 06:34 PM, Andi Kleen wrote:
> On Tuesday 26 June 2007 00:05:17 Chuck Ebbert wrote:
>> On 06/25/2007 05:38 PM, Loic Prylli wrote:
>>
>> [cc: Andi]
>>
>>> Processors synchronization in set_mtrr requires the .gate field
>>> to be set after .count field is properly initialized. Without an explicit
>>> barrier, the compiler was reordering those memory stores. That was sometimes
>>> causing a processor (in ipi_handler) to see the .gate change and
>>> decrement .count before the latter is set by set_mtrr() (which
>>> then hangs in a infinite loop with irqs disabled).
> 
> Hmm, perhaps we should just put the smp_wmb into atomic_set().
> Near all other atomic operations have memory barriers too. I think
> that would be the better fix.

Can we get something merged before 2.6.22-final?

The original patch seems okay...
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