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Date: Sun, 29 Aug 2010 21:38:27 +0300
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Subject: Re: [PATCH 05/11] x86-64: Disable preemption when using TS_USEDFPU
From: Pekka Enberg <penberg@kernel.org>
To: Brian Gerst <brgerst@gmail.com>
Cc: hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org
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On Sat, Aug 28, 2010 at 7:04 PM, Brian Gerst <brgerst@gmail.com> wrote:
> Consolidates code and fixes the below race for 64-bit.
>
> commit 9fa2f37bfeb798728241cc4a19578ce6e4258f25
> Author: torvalds <torvalds>
> Date: ? Tue Sep 2 07:37:25 2003 +0000
>
> ? ?Be a lot more careful about TS_USEDFPU and preemption
>
> ? ?We had some races where we testecd (or set) TS_USEDFPU together
> ? ?with sequences that depended on the setting (like clearing or
> ? ?setting the TS flag in %cr0) and we could be preempted in between,
> ? ?which screws up the FPU state, since preemption will itself change
> ? ?USEDFPU and the TS flag.
>
> ? ?This makes it a lot more explicit: the "internal" low-level FPU
> ? ?functions ("__xxxx_fpu()") all require preemption to be disabled,
> ? ?and the exported "real" functions will make sure that is the case.
>
> ? ?One case - in __switch_to() - was switched to the non-preempt-safe
> ? ?internal version, since the scheduler itself has already disabled
> ? ?preemption.
>
> ? ?BKrev: 3f5448b5WRiQuyzAlbajs3qoQjSobw
>
> Signed-off-by: Brian Gerst <brgerst@gmail.com>

Acked-by: Pekka Enberg <penberg@kernel.org>
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