Commit cff5f49d authored by Tim Van Patten's avatar Tim Van Patten Committed by Tejun Heo
Browse files

cgroup_freezer: cgroup_freezing: Check if not frozen 



__thaw_task() was recently updated to warn if the task being thawed was
part of a freezer cgroup that is still currently freezing:

	void __thaw_task(struct task_struct *p)
	{
	...
		if (WARN_ON_ONCE(freezing(p)))
			goto unlock;

This has exposed a bug in cgroup1 freezing where when CGROUP_FROZEN is
asserted, the CGROUP_FREEZING bits are not also cleared at the same
time. Meaning, when a cgroup is marked FROZEN it continues to be marked
FREEZING as well. This causes the WARNING to trigger, because
cgroup_freezing() thinks the cgroup is still freezing.

There are two ways to fix this:

1. Whenever FROZEN is set, clear FREEZING for the cgroup and all
children cgroups.
2. Update cgroup_freezing() to also verify that FROZEN is not set.

This patch implements option (2), since it's smaller and more
straightforward.

Signed-off-by: default avatarTim Van Patten <timvp@google.com>
Tested-by: default avatarMark Hasemeyer <markhas@chromium.org>
Fixes: f5d39b02 ("freezer,sched: Rewrite core freezer logic")
Cc: stable@vger.kernel.org # v6.1+
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 037266a5

kernel/cgroup/legacy_freezer.c

+7 −1
Original line number Diff line number Diff line
@@ -66,9 +66,15 @@ static struct freezer *parent_freezer(struct freezer *freezer) 
bool cgroup_freezing(struct task_struct *task)

{

	bool ret;

	unsigned int state;



	rcu_read_lock();

	ret = task_freezer(task)->state & CGROUP_FREEZING;

	/* Check if the cgroup is still FREEZING, but not FROZEN. The extra

	 * !FROZEN check is required, because the FREEZING bit is not cleared

	 * when the state FROZEN is reached.

	 */

	state = task_freezer(task)->state;

	ret = (state & CGROUP_FREEZING) && !(state & CGROUP_FROZEN);

	rcu_read_unlock();



	return ret;