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Subject[PATCH RFC] fix RCU-callback-after-kmem_cache_destroy problem in sl[aou]b
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@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) {

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