1 files changed, 25 insertions, 30 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 497ec33ff22d..13b9d0f221b8 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -54,6 +54,7 @@
 #include <linux/page_cgroup.h>
 #include <linux/cpu.h>
 #include <linux/oom.h>
+#include <linux/lockdep.h>
 #include "internal.h"
 #include <net/sock.h>
 #include <net/ip.h>
@@ -2046,6 +2047,12 @@ static int mem_cgroup_soft_reclaim(struct mem_cgroup *root_memcg,
         return total;
 }
 
+#ifdef CONFIG_LOCKDEP
+static struct lockdep_map memcg_oom_lock_dep_map = {
+        .name = "memcg_oom_lock",
+};
+#endif
+
 static DEFINE_SPINLOCK(memcg_oom_lock);
 
 /*
@@ -2083,7 +2090,8 @@ static bool mem_cgroup_oom_trylock(struct mem_cgroup *memcg)
                         }
                         iter->oom_lock = false;
                 }
-        }
+        } else
+                mutex_acquire(&memcg_oom_lock_dep_map, 0, 1, _RET_IP_);
 
         spin_unlock(&memcg_oom_lock);
 
@@ -2095,6 +2103,7 @@ static void mem_cgroup_oom_unlock(struct mem_cgroup *memcg)
         struct mem_cgroup *iter;
 
         spin_lock(&memcg_oom_lock);
+        mutex_release(&memcg_oom_lock_dep_map, 1, _RET_IP_);
         for_each_mem_cgroup_tree(iter, memcg)
                 iter->oom_lock = false;
         spin_unlock(&memcg_oom_lock);
@@ -2765,10 +2774,10 @@ done:
         *ptr = memcg;
         return 0;
 nomem:
-        *ptr = NULL;
-        if (gfp_mask & __GFP_NOFAIL)
-                return 0;
-        return -ENOMEM;
+        if (!(gfp_mask & __GFP_NOFAIL)) {
+                *ptr = NULL;
+                return -ENOMEM;
+        }
 bypass:
         *ptr = root_mem_cgroup;
         return -EINTR;
@@ -3773,7 +3782,6 @@ void mem_cgroup_move_account_page_stat(struct mem_cgroup *from,
 {
         /* Update stat data for mem_cgroup */
         preempt_disable();
-        WARN_ON_ONCE(from->stat->count[idx] < nr_pages);
         __this_cpu_sub(from->stat->count[idx], nr_pages);
         __this_cpu_add(to->stat->count[idx], nr_pages);
         preempt_enable();
@@ -4950,31 +4958,18 @@ static void mem_cgroup_reparent_charges(struct mem_cgroup *memcg)
         } while (usage > 0);
 }
 
-/*
- * This mainly exists for tests during the setting of set of use_hierarchy.
- * Since this is the very setting we are changing, the current hierarchy value
- * is meaningless
- */
-static inline bool __memcg_has_children(struct mem_cgroup *memcg)
-{
-        struct cgroup_subsys_state *pos;
-
-        /* bounce at first found */
-        css_for_each_child(pos, &memcg->css)
-                return true;
-        return false;
-}
-
-/*
- * Must be called with memcg_create_mutex held, unless the cgroup is guaranteed
- * to be already dead (as in mem_cgroup_force_empty, for instance).  This is
- * from mem_cgroup_count_children(), in the sense that we don't really care how
- * many children we have; we only need to know if we have any.  It also counts
- * any memcg without hierarchy as infertile.
- */
 static inline bool memcg_has_children(struct mem_cgroup *memcg)
 {
-        return memcg->use_hierarchy && __memcg_has_children(memcg);
+        lockdep_assert_held(&memcg_create_mutex);
+        /*
+         * The lock does not prevent addition or deletion to the list
+         * of children, but it prevents a new child from being
+         * initialized based on this parent in css_online(), so it's
+         * enough to decide whether hierarchically inherited
+         * attributes can still be changed or not.
+         */
+        return memcg->use_hierarchy &&
+                !list_empty(&memcg->css.cgroup->children);
 }
 
 /*
@@ -5054,7 +5049,7 @@ static int mem_cgroup_hierarchy_write(struct cgroup_subsys_state *css,
          */
         if ((!parent_memcg || !parent_memcg->use_hierarchy) &&
                                 (val == 1 || val == 0)) {
-                if (!__memcg_has_children(memcg))
+                if (list_empty(&memcg->css.cgroup->children))
                         memcg->use_hierarchy = val;
                 else
                         retval = -EBUSY;