cgroup,freezer: fix incomplete freezing when attaching tasks

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")
Cc: stable@vger.kernel.org # v6.1+
Reported-by: Zhong Jiawei <zhongjiawei1@huawei.com>
Signed-off-by: Chen Ridong <chenridong@huawei.com>
Acked-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup/legacy_freezer.c b/kernel/cgroup/legacy_freezer.c
index 039d1eb2f215bb929514b8239575de5b0eb0cdc6..507b8f19a262e06460707ef0e543a7ab94cb39d9 100644 (file)
--- 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);
                }
        }