Re: [PATCH RFC] fix RCU-callback-after-kmem_cache_destroy problem in sl[aou]b

Nick Piggin
2009-06-26T09:04:05Z

On Thu, Jun 25, 2009 at 04:27:19PM -0500, Matt Mackall wrote:
> On Thu, 2009-06-25 at 12:31 -0700, Paul E. McKenney wrote:
> > Hello!
> >
> > Jesper noted that kmem_cache_destroy() invokes synchronize_rcu() rather
> > than rcu_barrier() in the SLAB_DESTROY_BY_RCU case, which could result
> > in RCU callbacks accessing a kmem_cache after it had been destroyed.
> >
> > The following untested (might not even compile) patch proposes a fix.
>
> Acked-by: Matt Mackall <mpm@selenic.com>
>
> Nick, you'll want to make sure you get this in SLQB.

Thanks Matt. Paul, I think this should be appropriate for
stable@kernel.org too?

>
> > Reported-by: Jesper Dangaard Brouer <jdb@comx.dk>
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > ---
> >
> > slab.c | 2 +-
> > slob.c | 2 ++
> > slub.c | 2 ++
> > 3 files changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/slab.c b/mm/slab.c
> > index e74a16e..5241b65 100644
> > --- a/mm/slab.c
> > +++ b/mm/slab.c
> > @@ -2547,7 +2547,7 @@ void kmem_cache_destroy(struct kmem_cache *cachep)
> > }
> >
> > if (unlikely(cachep->flags & SLAB_DESTROY_BY_RCU))
> > - synchronize_rcu();
> > + rcu_barrier();
> >
> > __kmem_cache_destroy(cachep);
> > mutex_unlock(&cache_chain_mutex);
> > diff --git a/mm/slob.c b/mm/slob.c
> > index c78742d..9641da3 100644
> > --- a/mm/slob.c
> > +++ b/mm/slob.c
> > @@ -595,6 +595,8 @@ EXPORT_SYMBOL(kmem_cache_create);
> > void kmem_cache_destroy(struct kmem_cache *c)
> > {
> > kmemleak_free(c);
> > + if (c->flags & SLAB_DESTROY_BY_RCU)
> > + rcu_barrier();
> > slob_free(c, sizeof(struct kmem_cache));
> > }
> > EXPORT_SYMBOL(kmem_cache_destroy);
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 819f056..a9201d8 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -2595,6 +2595,8 @@ static inline int kmem_cache_close(struct kmem_cache *s)
> > */
> > void kmem_cache_destroy(struct kmem_cache *s)
> > {
> > + if (s->flags & SLAB_DESTROY_BY_RCU)
> > + rcu_barrier();
> > down_write(&slub_lock);
> > s->refcount--;
> > if (!s->refcount) {
>
> --
> http://selenic.com : development and support for Mercurial and Linux
>