Date: Mon, 7 May 2012 15:24:06 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
To: Pekka Enberg <penberg@kernel.org>
cc: Andi Kleen <andi@firstfloor.org>, linux-kernel@vger.kernel.org,
        Andi Kleen <ak@linux.intel.com>, David Rientjes <rientjes@google.com>,
        linux-mm@kvack.org
Subject: Re: [PATCH] slab/mempolicy: always use local policy from interrupt
 context v2
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On Thu, 3 May 2012, Pekka Enberg wrote:

> (Adding some CC's.)

Uggg... Strange whitespace coming from Pekka again.

> On Sun, Apr 15, 2012 at 5:22 PM, Andi Kleen <andi@firstfloor.org> wrote:
> > From: Andi Kleen <ak@linux.intel.com>
> >
> > slab_node() could access current->mempolicy from interrupt context.
> > However there's a race condition during exit where the mempolicy
> > is first freed and then the pointer zeroed.
> >
> > Using this from interrupts seems bogus anyways. The interrupt
> > will interrupt a random process and therefore get a random
> > mempolicy. Many times, this will be idle's, which noone can change.
> >
> > Just disable this here and always use local for slab
> > from interrupts. I also cleaned up the callers of slab_node a bit
> > which always passed the same argument.

Good idea.

> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index cfb6c86..da79bbf 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -1586,8 +1586,9 @@ static unsigned interleave_nodes(struct mempolicy=
 *policy)
> > =A0* task can change it's policy. =A0The system default policy requires=
 no
> > =A0* such protection.
> > =A0*/
> > -unsigned slab_node(struct mempolicy *policy)
> > +unsigned slab_node(void)
> > =A0{
> > + =A0 =A0 =A0 struct mempolicy *policy =3D !in_interrupt() ? current->p=
olicy : NULL;
> > =A0 =A0 =A0 =A0if (!policy || policy->flags & MPOL_F_LOCAL)

Simplify this to if (in_interrupt() || !policy || .... ?

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