[PATCH 1/6] cgroup_freezer: fix freezer->state setting bug in freezer_change_state()

[Tejun Heo]

d02f52811d0e "cgroup_freezer: prepare for removal of TIF_FREEZE" moved
setting of freezer->state into freezer_change_state(); unfortunately,
while doing so, when it's beginning to freeze tasks, it sets the state
to CGROUP_FROZEN instead of CGROUP_FREEZING ending up skipping the
whole freezing state.  Fix it.

-v2: Oleg pointed out that re-freezing FROZEN cgroup could increment
     system_freezing_cnt.  Fixed.

-v3: Matt pointed out that setting CGROUP_FROZEN always invoked
     try_to_freeze_cgroup() regardless of the current state.  Patch
     updated such that the actual freeze/thaw operations are always
     performed on state changes.  This shouldn't make any difference
     unless something is broken.

Signed-off-by: Tejun Heo <tj at kernel.org>
Reported-by: Oleg Nesterov <oleg at redhat.com>
Cc: Paul Menage <paul at paulmenage.org>
Cc: "Rafael J. Wysocki" <rjw at sisk.pl>
Cc: Matt Helsley <matthltc at us.ibm.com>
---
 kernel/cgroup_freezer.c |   14 +++++++-------
 1 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 4e82525..56a457a 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -308,24 +308,24 @@ static int freezer_change_state(struct cgroup *cgroup,
 	spin_lock_irq(&freezer->lock);
 
 	update_if_frozen(cgroup, freezer);
-	if (goal_state == freezer->state)
-		goto out;
-
-	freezer->state = goal_state;
 
 	switch (goal_state) {
 	case CGROUP_THAWED:
-		atomic_dec(&system_freezing_cnt);
+		if (freezer->state != CGROUP_THAWED)
+			atomic_dec(&system_freezing_cnt);
+		freezer->state = CGROUP_THAWED;
 		unfreeze_cgroup(cgroup, freezer);
 		break;
 	case CGROUP_FROZEN:
-		atomic_inc(&system_freezing_cnt);
+		if (freezer->state == CGROUP_THAWED)
+			atomic_inc(&system_freezing_cnt);
+		freezer->state = CGROUP_FREEZING;
 		retval = try_to_freeze_cgroup(cgroup, freezer);
 		break;
 	default:
 		BUG();
 	}
-out:
+
 	spin_unlock_irq(&freezer->lock);
 
 	return retval;
-- 
1.7.6