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>

1 files changed, 2 insertions, 2 deletions

diff --git a/mm/slub.c b/mm/slub.c
index b9f1491a58a..b6276753626 100644
--- 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);