From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754563Ab3LRNRL (ORCPT ); Wed, 18 Dec 2013 08:17:11 -0500 Received: from relay.parallels.com ([195.214.232.42]:54269 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754301Ab3LRNRF (ORCPT ); Wed, 18 Dec 2013 08:17:05 -0500 From: Vladimir Davydov To: Michal Hocko CC: , , , , Johannes Weiner , Glauber Costa , Christoph Lameter , Pekka Enberg , Andrew Morton Subject: [PATCH 5/6] memcg: clear memcg_params after removing cache from memcg_slab_caches list Date: Wed, 18 Dec 2013 17:16:56 +0400 Message-ID: X-Mailer: git-send-email 1.7.10.4 In-Reply-To: <6f02b2d079ffd0990ae335339c803337b13ecd8c.1387372122.git.vdavydov@parallels.com> References: <6f02b2d079ffd0990ae335339c803337b13ecd8c.1387372122.git.vdavydov@parallels.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.30.16.96] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org All caches of the same memory cgroup are linked in the memcg_slab_caches list via kmem_cache::memcg_params::list. This list is traversed when we read memory.kmem.slabinfo. Since the list actually consists of memcg_cache_params objects, to convert an element of the list to a kmem_cache object, we use memcg_params_to_cache(), which obtains the pointer to the cache from the memcg_params::memcg_caches array of the root cache, but on cache destruction this pointer is cleared before the removal of the cache from the list, which potentially can result in a NULL ptr dereference. Let's fix this by clearing the pointer to a cache in the memcg_params::memcg_caches array of its parent only after it cannot be accessed by the memcg_slab_caches list. Signed-off-by: Vladimir Davydov Cc: Michal Hocko Cc: Johannes Weiner Cc: Glauber Costa Cc: Christoph Lameter Cc: Pekka Enberg Cc: Andrew Morton --- mm/memcontrol.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 62b9991..ad8de6a 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3241,6 +3241,11 @@ void memcg_register_cache(struct kmem_cache *s) */ smp_wmb(); + /* + * Initialize the pointer to this cache in its parent's memcg_params + * before adding it to the memcg_slab_caches list, otherwise we can + * fail to convert memcg_params_to_cache() while traversing the list. + */ root->memcg_params->memcg_caches[id] = s; mutex_lock(&memcg->slab_caches_mutex); @@ -3265,15 +3270,20 @@ void memcg_release_cache(struct kmem_cache *s) goto out; memcg = s->memcg_params->memcg; - id = memcg_cache_id(memcg); - + id = memcg_cache_id(memcg); root = s->memcg_params->root_cache; - root->memcg_params->memcg_caches[id] = NULL; mutex_lock(&memcg->slab_caches_mutex); list_del(&s->memcg_params->list); mutex_unlock(&memcg->slab_caches_mutex); + /* + * Clear the pointer to this cache in its parent's memcg_params only + * after removing it from the memcg_slab_caches list, otherwise we can + * fail to convert memcg_params_to_cache() while traversing the list. + */ + root->memcg_params->memcg_caches[id] = NULL; + css_put(&memcg->css); out: kfree(s->memcg_params); -- 1.7.10.4