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

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Date:	Tue, 26 Jun 2007 00:34:41 +0200
From:	Andi Kleen <ak@...e.de>
To:	Chuck Ebbert <cebbert@...hat.com>
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 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.

-Andi
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