Patch "cgroup_freezer: cgroup_freezing: Check if not frozen" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    cgroup_freezer: cgroup_freezing: Check if not frozen

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     cgroup_freezer-cgroup_freezing-check-if-not-frozen.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From cff5f49d433fcd0063c8be7dd08fa5bf190c6c37 Mon Sep 17 00:00:00 2001
From: Tim Van Patten <timvp@xxxxxxxxxx>
Date: Wed, 15 Nov 2023 09:20:43 -0700
Subject: cgroup_freezer: cgroup_freezing: Check if not frozen

From: Tim Van Patten <timvp@xxxxxxxxxx>

commit cff5f49d433fcd0063c8be7dd08fa5bf190c6c37 upstream.

__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@xxxxxxxxxx>
Tested-by: Mark Hasemeyer <markhas@xxxxxxxxxxxx>
Fixes: f5d39b020809 ("freezer,sched: Rewrite core freezer logic")
Cc: stable@xxxxxxxxxxxxxxx # v6.1+
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/cgroup/legacy_freezer.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/legacy_freezer.c b/kernel/cgroup/legacy_freezer.c
index 122dacb3a443..66d1708042a7 100644
--- 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;
-- 
2.43.0



Patches currently in stable-queue which might be from timvp@xxxxxxxxxx are

queue-6.1/cgroup_freezer-cgroup_freezing-check-if-not-frozen.patch




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