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: Tim Van Patten <timvp@google.com>
Tested-by: Mark Hasemeyer <markhas@chromium.org>
Fixes: f5d39b020809 ("freezer,sched: Rewrite core freezer logic")
Cc: stable@vger.kernel.org # v6.1+
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup/legacy_freezer.c b/kernel/cgroup/legacy_freezer.c
index 122dacb3a44390825054d67530f8f894f2f7fb04..66d1708042a72bf5d25b9ff1d7acb8d91183ffd7 100644 (file)
--- a/kernel/cgroup/legacy_freezer.c
+++ b/kernel/cgroup/legacy_freezer.c
@@ -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;