tree: git://git.cmpxchg.org/linux-mmotm.git master head: c64429bcc60a702f19f5cfdb5c39277863278a8c commit: 5d06629c100b942a51f02b4d886c116ba3afb32a [200/417] slab: embed memcg_cache_params to kmem_cache mm/slab_common.c:166 update_memcg_params() warn: variable dereferenced before check 'old' (see line 162) git remote add mmotm git://git.cmpxchg.org/linux-mmotm.git git remote update mmotm git checkout 5d06629c100b942a51f02b4d886c116ba3afb32a vim +/old +166 mm/slab_common.c 5d06629c Vladimir Davydov 2015-01-24 156 lockdep_is_held(&slab_mutex)); 5d06629c Vladimir Davydov 2015-01-24 157 new = kzalloc(sizeof(struct memcg_cache_array) + 5d06629c Vladimir Davydov 2015-01-24 158 new_array_size * sizeof(void *), GFP_KERNEL); 5d06629c Vladimir Davydov 2015-01-24 159 if (!new) 6f817f4c Vladimir Davydov 2014-10-09 160 return -ENOMEM; 6f817f4c Vladimir Davydov 2014-10-09 161 5d06629c Vladimir Davydov 2015-01-24 @162 memcpy(new->entries, old->entries, 88a0b848 Vladimir Davydov 2015-01-24 163 memcg_nr_cache_ids * sizeof(void *)); 6f817f4c Vladimir Davydov 2014-10-09 164 5d06629c Vladimir Davydov 2015-01-24 165 rcu_assign_pointer(s->memcg_params.memcg_caches, new); 5d06629c Vladimir Davydov 2015-01-24 @166 if (old) 5d06629c Vladimir Davydov 2015-01-24 167 kfree_rcu(old, rcu); 6f817f4c Vladimir Davydov 2014-10-09 168 return 0; 6f817f4c Vladimir Davydov 2014-10-09 169 } This warning is false-positive, because @old equals NULL iff @memcg_nr_cache_ids equals 0. Moreover, this function had been acting in exactly the same fashion before it was reworked by the culprit. Anyways, let's add an explicit check if @old is not NULL before passing it to @memcpy() to make static analysis tools happy. fixes: slab-embed-memcg_cache_params-to-kmem_cache Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx> Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx> --- mm/slab_common.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/mm/slab_common.c b/mm/slab_common.c index bf4a42b2c5ba..0dd9eb4e0f87 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -153,15 +153,16 @@ static int update_memcg_params(struct kmem_cache *s, int new_array_size) if (!is_root_cache(s)) return 0; - old = rcu_dereference_protected(s->memcg_params.memcg_caches, - lockdep_is_held(&slab_mutex)); new = kzalloc(sizeof(struct memcg_cache_array) + new_array_size * sizeof(void *), GFP_KERNEL); if (!new) return -ENOMEM; - memcpy(new->entries, old->entries, - memcg_nr_cache_ids * sizeof(void *)); + old = rcu_dereference_protected(s->memcg_params.memcg_caches, + lockdep_is_held(&slab_mutex)); + if (old) + memcpy(new->entries, old->entries, + memcg_nr_cache_ids * sizeof(void *)); rcu_assign_pointer(s->memcg_params.memcg_caches, new); if (old) -- 1.7.10.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>