[next] cgroup,freezer: fix incomplete freezing when attaching tasks

[Chen Ridong]

From: Chen Ridong <chenridong@xxxxxxxxxx>

An issue was found:

	# cd /sys/fs/cgroup/freezer/
	# mkdir test
	# echo FROZEN > test/freezer.state
	# cat test/freezer.state
	FROZEN
	# sleep 1000 &
	[1] 863
	# echo 863 > test/cgroup.procs
	# cat test/freezer.state
	FREEZING

When tasks are migrated to a frozen cgroup, the freezer fails to
immediately freeze the tasks, causing the cgroup to remain in the
"FREEZING".

The freeze_task() function is called before clearing the CGROUP_FROZEN
flag. This causes the freezing() check to incorrectly return false,
preventing __freeze_task() from being invoked for the migrated task.

To fix this issue, clear the CGROUP_FROZEN state before calling
freeze_task().

Fixes: f5d39b020809 ("freezer,sched: Rewrite core freezer logic")
Reported-by: Zhong Jiawei <zhongjiawei1@xxxxxxxxxx>
Signed-off-by: Chen Ridong <chenridong@xxxxxxxxxx>
---
 kernel/cgroup/legacy_freezer.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/cgroup/legacy_freezer.c b/kernel/cgroup/legacy_freezer.c
index 039d1eb2f215..507b8f19a262 100644
--- a/kernel/cgroup/legacy_freezer.c
+++ b/kernel/cgroup/legacy_freezer.c
@@ -188,13 +188,12 @@ static void freezer_attach(struct cgroup_taskset *tset)
 		if (!(freezer->state & CGROUP_FREEZING)) {
 			__thaw_task(task);
 		} else {
-			freeze_task(task);
-
 			/* clear FROZEN and propagate upwards */
 			while (freezer && (freezer->state & CGROUP_FROZEN)) {
 				freezer->state &= ~CGROUP_FROZEN;
 				freezer = parent_freezer(freezer);
 			}
+			freeze_task(task);
 		}
 	}
 
-- 
2.34.1