linux-kernel - Re: [PATCH] x86, fpu: __restore_xstate_sig()->math_state_restore() needs preempt

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Date:	Mon, 1 Sep 2014 22:01:46 -0700
From:	Suresh Siddha <sbsiddha@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Bean Anderson <bean@...lsystems.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, fpu: __restore_xstate_sig()->math_state_restore()
 needs preempt_disable()

On Mon, Aug 25, 2014 at 11:08 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> Add preempt_disable() + preempt_enable() around math_state_restore() in
> __restore_xstate_sig(). Otherwise __switch_to() after __thread_fpu_begin()
> can overwrite fpu->state we are going to restore.
>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> Cc: stable@...r.kernel.org
> ---
>  arch/x86/kernel/xsave.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
> index 453343c..c52eb9c 100644
> --- a/arch/x86/kernel/xsave.c
> +++ b/arch/x86/kernel/xsave.c
> @@ -397,8 +397,11 @@ int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)
>                         set_used_math();
>                 }
>
> -               if (use_eager_fpu())
> +               if (use_eager_fpu()) {
> +                       preempt_disable();
>                         math_state_restore();
> +                       preempt_enable();
> +               }
>
>                 return err;
>         } else {
>

oops. looks good to me.

Reviewed-by: Suresh Siddha <sbsiddha@...il.com>
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