1 files changed, 46 insertions, 37 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0980bbf6438..04250cbf46c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1916,15 +1916,18 @@ mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg,
 	return SKIP;
 }
 
+static DEFINE_SPINLOCK(memcg_oom_lock);
+
 /*
  * Check OOM-Killer is already running under our hierarchy.
  * If someone is running, return false.
- * Has to be called with memcg_oom_lock
  */
-static bool mem_cgroup_oom_lock(struct mem_cgroup *memcg)
+static bool mem_cgroup_oom_trylock(struct mem_cgroup *memcg)
 {
 	struct mem_cgroup *iter, *failed = NULL;
 
+	spin_lock(&memcg_oom_lock);
+
 	for_each_mem_cgroup_tree(iter, memcg) {
 		if (iter->oom_lock) {
 			/*
@@ -1938,33 +1941,33 @@ static bool mem_cgroup_oom_lock(struct mem_cgroup *memcg)
 			iter->oom_lock = true;
 	}
 
-	if (!failed)
-		return true;
-
-	/*
-	 * OK, we failed to lock the whole subtree so we have to clean up
-	 * what we set up to the failing subtree
-	 */
-	for_each_mem_cgroup_tree(iter, memcg) {
-		if (iter == failed) {
-			mem_cgroup_iter_break(memcg, iter);
-			break;
+	if (failed) {
+		/*
+		 * OK, we failed to lock the whole subtree so we have
+		 * to clean up what we set up to the failing subtree
+		 */
+		for_each_mem_cgroup_tree(iter, memcg) {
+			if (iter == failed) {
+				mem_cgroup_iter_break(memcg, iter);
+				break;
+			}
+			iter->oom_lock = false;
 		}
-		iter->oom_lock = false;
 	}
-	return false;
+
+	spin_unlock(&memcg_oom_lock);
+
+	return !failed;
 }
 
-/*
- * Has to be called with memcg_oom_lock
- */
-static int mem_cgroup_oom_unlock(struct mem_cgroup *memcg)
+static void mem_cgroup_oom_unlock(struct mem_cgroup *memcg)
 {
 	struct mem_cgroup *iter;
 
+	spin_lock(&memcg_oom_lock);
 	for_each_mem_cgroup_tree(iter, memcg)
 		iter->oom_lock = false;
-	return 0;
+	spin_unlock(&memcg_oom_lock);
 }
 
 static void mem_cgroup_mark_under_oom(struct mem_cgroup *memcg)
@@ -1988,7 +1991,6 @@ static void mem_cgroup_unmark_under_oom(struct mem_cgroup *memcg)
 		atomic_add_unless(&iter->under_oom, -1, 0);
 }
 
-static DEFINE_SPINLOCK(memcg_oom_lock);
 static DECLARE_WAIT_QUEUE_HEAD(memcg_oom_waitq);
 
 struct oom_wait_info {
@@ -2035,45 +2037,52 @@ static bool mem_cgroup_handle_oom(struct mem_cgroup *memcg, gfp_t mask,
 				  int order)
 {
 	struct oom_wait_info owait;
-	bool locked, need_to_kill;
+	bool locked;
 
 	owait.memcg = memcg;
 	owait.wait.flags = 0;
 	owait.wait.func = memcg_oom_wake_function;
 	owait.wait.private = current;
 	INIT_LIST_HEAD(&owait.wait.task_list);
-	need_to_kill = true;
-	mem_cgroup_mark_under_oom(memcg);
 
-	/* At first, try to OOM lock hierarchy under memcg.*/
-	spin_lock(&memcg_oom_lock);
-	locked = mem_cgroup_oom_lock(memcg);
 	/*
+	 * As with any blocking lock, a contender needs to start
+	 * listening for wakeups before attempting the trylock,
+	 * otherwise it can miss the wakeup from the unlock and sleep
+	 * indefinitely.  This is just open-coded because our locking
+	 * is so particular to memcg hierarchies.
+	 *
 	 * Even if signal_pending(), we can't quit charge() loop without
 	 * accounting. So, UNINTERRUPTIBLE is appropriate. But SIGKILL
 	 * under OOM is always welcomed, use TASK_KILLABLE here.
 	 */
 	prepare_to_wait(&memcg_oom_waitq, &owait.wait, TASK_KILLABLE);
-	if (!locked || memcg->oom_kill_disable)
-		need_to_kill = false;
+	mem_cgroup_mark_under_oom(memcg);
+
+	locked = mem_cgroup_oom_trylock(memcg);
+
 	if (locked)
 		mem_cgroup_oom_notify(memcg);
-	spin_unlock(&memcg_oom_lock);
 
-	if (need_to_kill) {
+	if (locked && !memcg->oom_kill_disable) {
+		mem_cgroup_unmark_under_oom(memcg);
 		finish_wait(&memcg_oom_waitq, &owait.wait);
 		mem_cgroup_out_of_memory(memcg, mask, order);
 	} else {
 		schedule();
+		mem_cgroup_unmark_under_oom(memcg);
 		finish_wait(&memcg_oom_waitq, &owait.wait);
 	}
-	spin_lock(&memcg_oom_lock);
-	if (locked)
-		mem_cgroup_oom_unlock(memcg);
-	memcg_wakeup_oom(memcg);
-	spin_unlock(&memcg_oom_lock);
 
-	mem_cgroup_unmark_under_oom(memcg);
+	if (locked) {
+		mem_cgroup_oom_unlock(memcg);
+		/*
+		 * There is no guarantee that an OOM-lock contender
+		 * sees the wakeups triggered by the OOM kill
+		 * uncharges.  Wake any sleepers explicitely.
+		 */
+		memcg_oom_recover(memcg);
+	}
 
 	if (test_thread_flag(TIF_MEMDIE) || fatal_signal_pending(current))
 		return false;