1 files changed, 32 insertions, 40 deletions

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index ce71ed5..e7bebb7 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -48,20 +48,19 @@ static inline struct freezer *task_freezer(struct task_struct *task)
 			    struct freezer, css);
 }
 
-int cgroup_freezing_or_frozen(struct task_struct *task)
+static inline int __cgroup_freezing_or_frozen(struct task_struct *task)
 {
-	struct freezer *freezer;
-	enum freezer_state state;
+	enum freezer_state state = task_freezer(task)->state;
+	return (state == CGROUP_FREEZING) || (state == CGROUP_FROZEN);
+}
 
+int cgroup_freezing_or_frozen(struct task_struct *task)
+{
+	int result;
 	task_lock(task);
-	freezer = task_freezer(task);
-	if (!freezer->css.cgroup->parent)
-		state = CGROUP_THAWED; /* root cgroup can't be frozen */
-	else
-		state = freezer->state;
+	result = __cgroup_freezing_or_frozen(task);
 	task_unlock(task);
-
-	return (state == CGROUP_FREEZING) || (state == CGROUP_FROZEN);
+	return result;
 }
 
 /*
@@ -154,13 +153,6 @@ static void freezer_destroy(struct cgroup_subsys *ss,
 	kfree(cgroup_freezer(cgroup));
 }
 
-/* Task is frozen or will freeze immediately when next it gets woken */
-static bool is_task_frozen_enough(struct task_struct *task)
-{
-	return frozen(task) ||
-		(task_is_stopped_or_traced(task) && freezing(task));
-}
-
 /*
  * The call to cgroup_lock() in the freezer.state write method prevents
  * a write to that file racing against an attach, and hence the
@@ -174,24 +166,25 @@ static int freezer_can_attach(struct cgroup_subsys *ss,
 
 	/*
 	 * Anything frozen can't move or be moved to/from.
-	 *
-	 * Since orig_freezer->state == FROZEN means that @task has been
-	 * frozen, so it's sufficient to check the latter condition.
 	 */
 
-	if (is_task_frozen_enough(task))
+	freezer = cgroup_freezer(new_cgroup);
+	if (freezer->state != CGROUP_THAWED)
 		return -EBUSY;
 
-	freezer = cgroup_freezer(new_cgroup);
-	if (freezer->state == CGROUP_FROZEN)
+	rcu_read_lock();
+	if (__cgroup_freezing_or_frozen(task)) {
+		rcu_read_unlock();
 		return -EBUSY;
+	}
+	rcu_read_unlock();
 
 	if (threadgroup) {
 		struct task_struct *c;
 
 		rcu_read_lock();
 		list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
-			if (is_task_frozen_enough(c)) {
+			if (__cgroup_freezing_or_frozen(c)) {
 				rcu_read_unlock();
 				return -EBUSY;
 			}
@@ -236,31 +229,30 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
 /*
  * caller must hold freezer->lock
  */
-static void update_freezer_state(struct cgroup *cgroup,
+static void update_if_frozen(struct cgroup *cgroup,
 				 struct freezer *freezer)
 {
 	struct cgroup_iter it;
 	struct task_struct *task;
 	unsigned int nfrozen = 0, ntotal = 0;
+	enum freezer_state old_state = freezer->state;
 
 	cgroup_iter_start(cgroup, &it);
 	while ((task = cgroup_iter_next(cgroup, &it))) {
 		ntotal++;
-		if (is_task_frozen_enough(task))
+		if (frozen(task))
 			nfrozen++;
 	}
 
-	/*
-	 * Transition to FROZEN when no new tasks can be added ensures
-	 * that we never exist in the FROZEN state while there are unfrozen
-	 * tasks.
-	 */
-	if (nfrozen == ntotal)
-		freezer->state = CGROUP_FROZEN;
-	else if (nfrozen > 0)
-		freezer->state = CGROUP_FREEZING;
-	else
-		freezer->state = CGROUP_THAWED;
+	if (old_state == CGROUP_THAWED) {
+		BUG_ON(nfrozen > 0);
+	} else if (old_state == CGROUP_FREEZING) {
+		if (nfrozen == ntotal)
+			freezer->state = CGROUP_FROZEN;
+	} else { /* old_state == CGROUP_FROZEN */
+		BUG_ON(nfrozen != ntotal);
+	}
+
 	cgroup_iter_end(cgroup, &it);
 }
 
@@ -279,7 +271,7 @@ static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
 	if (state == CGROUP_FREEZING) {
 		/* We change from FREEZING to FROZEN lazily if the cgroup was
 		 * only partially frozen when we exitted write. */
-		update_freezer_state(cgroup, freezer);
+		update_if_frozen(cgroup, freezer);
 		state = freezer->state;
 	}
 	spin_unlock_irq(&freezer->lock);
@@ -301,7 +293,7 @@ static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
 	while ((task = cgroup_iter_next(cgroup, &it))) {
 		if (!freeze_task(task, true))
 			continue;
-		if (is_task_frozen_enough(task))
+		if (frozen(task))
 			continue;
 		if (!freezing(task) && !freezer_should_skip(task))
 			num_cant_freeze_now++;
@@ -335,7 +327,7 @@ static int freezer_change_state(struct cgroup *cgroup,
 
 	spin_lock_irq(&freezer->lock);
 
-	update_freezer_state(cgroup, freezer);
+	update_if_frozen(cgroup, freezer);
 	if (goal_state == freezer->state)
 		goto out;