Subject: [merged] memcg-fix-possible-null-deref-while-traversing-memcg_slab_caches-list.patch removed from -mm tree
To: vdavydov@xxxxxxxxxxxxx,bsingharora@xxxxxxxxx,glommer@xxxxxxxxx,hannes@xxxxxxxxxxx,kamezawa.hiroyu@xxxxxxxxxxxxxx,mhocko@xxxxxxx,mm-commits@xxxxxxxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Fri, 24 Jan 2014 10:58:43 -0800
The patch titled
Subject: memcg: fix possible NULL deref while traversing memcg_slab_caches list
has been removed from the -mm tree. Its filename was
memcg-fix-possible-null-deref-while-traversing-memcg_slab_caches-list.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Subject: memcg: fix possible NULL deref while traversing memcg_slab_caches list
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, for
example, when we read memory.kmem.slabinfo. Since the list actually
consists of memcg_cache_params objects, we have to convert an element of
the list to a kmem_cache object using memcg_params_to_cache(), which
obtains the pointer to the cache from the memcg_params::memcg_caches array
of the corresponding root cache. That said the pointer to a kmem_cache in
its parent's memcg_params must be initialized before adding the cache to
the list, and cleared only after it has been unlinked. Currently it is
vice-versa, which can result in a NULL ptr dereference while traversing
the memcg_slab_caches list. This patch restores the correct order.
Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Glauber Costa <glommer@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Balbir Singh <bsingharora@xxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 25 ++++++++++++++++++-------
1 file changed, 18 insertions(+), 7 deletions(-)
diff -puN mm/memcontrol.c~memcg-fix-possible-null-deref-while-traversing-memcg_slab_caches-list mm/memcontrol.c
--- a/mm/memcontrol.c~memcg-fix-possible-null-deref-while-traversing-memcg_slab_caches-list
+++ a/mm/memcontrol.c
@@ -3270,9 +3270,6 @@ void memcg_register_cache(struct kmem_ca
css_get(&memcg->css);
- mutex_lock(&memcg->slab_caches_mutex);
- list_add(&s->memcg_params->list, &memcg->memcg_slab_caches);
- mutex_unlock(&memcg->slab_caches_mutex);
/*
* Since readers won't lock (see cache_from_memcg_idx()), we need a
@@ -3281,7 +3278,16 @@ void memcg_register_cache(struct kmem_ca
*/
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);
+ list_add(&s->memcg_params->list, &memcg->memcg_slab_caches);
+ mutex_unlock(&memcg->slab_caches_mutex);
}
void memcg_unregister_cache(struct kmem_cache *s)
@@ -3293,16 +3299,21 @@ void memcg_unregister_cache(struct kmem_
if (is_root_cache(s))
return;
- memcg = s->memcg_params->memcg;
- id = memcg_cache_id(memcg);
-
root = s->memcg_params->root_cache;
- root->memcg_params->memcg_caches[id] = NULL;
+ memcg = s->memcg_params->memcg;
+ id = memcg_cache_id(memcg);
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);
}
_
Patches currently in -mm which might be from vdavydov@xxxxxxxxxxxxx are
origin.patch
mm-vmscan-respect-numa-policy-mask-when-shrinking-slab-on-direct-reclaim.patch
mm-vmscan-move-call-to-shrink_slab-to-shrink_zones.patch
mm-vmscan-remove-shrink_control-arg-from-do_try_to_free_pages.patch
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