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cgroup_freezer: cgroup_freezing: Check if not frozen

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__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: Tim Van Patten <timvp@google.com>
Tested-by: Mark Hasemeyer <markhas@chromium.org>
Fixes: f5d39b0208 ("freezer,sched: Rewrite core freezer logic")
Cc: stable@vger.kernel.org # v6.1+
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tim Van Patten 2023-11-15 09:20:43 -07:00 committed by Tejun Heo
parent 037266a5f7
commit cff5f49d43
1 changed files with 7 additions and 1 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

8
kernel/cgroup/legacy_freezer.c
View file

@ -66,9 +66,15 @@ static struct freezer *parent_freezer(struct freezer *freezer)
bool cgroup_freezing(struct task_struct *task) bool cgroup_freezing(struct task_struct *task)
{ {
bool ret; bool ret;
unsigned int state;
rcu_read_lock(); 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(); rcu_read_unlock();
return ret; return ret;