Commit 051dd460 authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Linus Torvalds
Browse files

memcg, slab: unregister cache from memcg before starting to destroy it 



Currently, memcg_unregister_cache(), which deletes the cache being
destroyed from the memcg_slab_caches list, is called after
__kmem_cache_shutdown() (see kmem_cache_destroy()), which starts to
destroy the cache.

As a result, one can access a partially destroyed cache while traversing
a memcg_slab_caches list, which can have deadly consequences (for
instance, cache_show() called for each cache on a memcg_slab_caches list
from mem_cgroup_slabinfo_read() will dereference pointers to already
freed data).

To fix this, let's move memcg_unregister_cache() before the cache
destruction process beginning, issuing memcg_register_cache() on failure.

Signed-off-by: default avatarVladimir Davydov <vdavydov@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Glauber Costa <glommer@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 794b1248

mm/memcontrol.c

+6 −6
Original line number Diff line number Diff line
@@ -3140,6 +3140,7 @@ int memcg_alloc_cache_params(struct mem_cgroup *memcg, struct kmem_cache *s, 
		s->memcg_params->root_cache = root_cache;

		INIT_WORK(&s->memcg_params->destroy,

				kmem_cache_destroy_work_func);

		css_get(&memcg->css);

	} else

		s->memcg_params->is_root_cache = true;
@@ -3148,6 +3149,10 @@ int memcg_alloc_cache_params(struct mem_cgroup *memcg, struct kmem_cache *s, 


void memcg_free_cache_params(struct kmem_cache *s)

{

	if (!s->memcg_params)

		return;

	if (!s->memcg_params->is_root_cache)

		css_put(&s->memcg_params->memcg->css);

	kfree(s->memcg_params);

}
@@ -3170,9 +3175,6 @@ void memcg_register_cache(struct kmem_cache *s) 
	memcg = s->memcg_params->memcg;

	id = memcg_cache_id(memcg);



	css_get(&memcg->css);





	/*

	 * Since readers won't lock (see cache_from_memcg_idx()), we need a

	 * barrier here to ensure nobody will see the kmem_cache partially
@@ -3221,10 +3223,8 @@ void memcg_unregister_cache(struct kmem_cache *s) 
	 * after removing it from the memcg_slab_caches list, otherwise we can

	 * fail to convert memcg_params_to_cache() while traversing the list.

	 */

	VM_BUG_ON(!root->memcg_params->memcg_caches[id]);

	VM_BUG_ON(root->memcg_params->memcg_caches[id] != s);

	root->memcg_params->memcg_caches[id] = NULL;



	css_put(&memcg->css);

}



/*

mm/slab_common.c

+2 −1
Original line number Diff line number Diff line
@@ -313,9 +313,9 @@ void kmem_cache_destroy(struct kmem_cache *s) 
	s->refcount--;

	if (!s->refcount) {

		list_del(&s->list);

		memcg_unregister_cache(s);



		if (!__kmem_cache_shutdown(s)) {

			memcg_unregister_cache(s);

			mutex_unlock(&slab_mutex);

			if (s->flags & SLAB_DESTROY_BY_RCU)

				rcu_barrier();
@@ -325,6 +325,7 @@ void kmem_cache_destroy(struct kmem_cache *s) 
			kmem_cache_free(kmem_cache, s);

		} else {

			list_add(&s->list, &slab_caches);

			memcg_register_cache(s);

			mutex_unlock(&slab_mutex);

			printk(KERN_ERR "kmem_cache_destroy %s: Slab cache still has objects\n",

				s->name);

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