slub: Fix kmem_cache_destroy() with SLAB_DESTROY_BY_RCU

kmem_cache_destroy() should call rcu_barrier() *after* kmem_cache_close() and
*before* sysfs_slab_remove() or risk rcu_free_slab() being called after
kmem_cache is deleted (kfreed).

rmmod nf_conntrack can crash the machine because it has to kmem_cache_destroy()
a SLAB_DESTROY_BY_RCU enabled cache.

Cc: <stable@kernel.org>
Reported-by: Zdenek Kabelac <zdenek.kabelac@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

diff --git a/mm/slub.c b/mm/slub.c
index b9f1491..b627675 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2594,8 +2594,6 @@ 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) {
@@ -2606,6 +2604,8 @@ void kmem_cache_destroy(struct kmem_cache *s)
                                "still has objects.\n", s->name, __func__);
                        dump_stack();
                }
+               if (s->flags & SLAB_DESTROY_BY_RCU)
+                       rcu_barrier();
                sysfs_slab_remove(s);
        } else
                up_write(&slub_lock);