[PATCH RFC] fix RCU-callback-after-kmem_cache_destroy problem insl[aou]b

[Paul E. McKenney]

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.

Reported-by: Jesper Dangaard Brouer <jdb@xxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---

 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) {
--
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