Re: [PATCH] slab/mempolicy: always use local policy from interruptcontext v2

[Christoph Lameter]

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@xxxxxxxxxxxxxx> wrote:
> > From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> >
> > 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)
> >  * task can change it's policy.  The system default policy requires no
> >  * such protection.
> >  */
> > -unsigned slab_node(struct mempolicy *policy)
> > +unsigned slab_node(void)
> >  {
> > +       struct mempolicy *policy = !in_interrupt() ? current->policy : NULL;
> >        if (!policy || policy->flags & MPOL_F_LOCAL)

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