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

Revert "cgroup_freezer: cgroup_freezing: Check if not frozen"

to the 6.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: revert-cgroup_freezer-cgroup_freezing-check-if-not-f.patch and it can be found in the queue-6.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

The patch ("sched,freezer: Remove unnecessary warning in __thaw_task") should also be merged to prevent triggering another warning in __thaw_task().

Best regards, Ridong

commit ee09694849a570cbc32015b5329b7c2f3f778748 Author: Chen Ridong chenridong@huawei.com Date: Thu Jul 17 08:55:50 2025 +0000

Revert "cgroup_freezer: cgroup_freezing: Check if not frozen"

[ Upstream commit 14a67b42cb6f3ab66f41603c062c5056d32ea7dd ] This reverts commit cff5f49d433fcd0063c8be7dd08fa5bf190c6c37. Commit cff5f49d433f ("cgroup_freezer: cgroup_freezing: Check if not frozen") modified the cgroup_freezing() logic to verify that the FROZEN flag is not set, affecting the return value of the freezing() function, in order to address a warning in __thaw_task. A race condition exists that may allow tasks to escape being frozen. The following scenario demonstrates this issue: CPU 0 (get_signal path) CPU 1 (freezer.state reader) try_to_freeze read freezer.state __refrigerator freezer_read update_if_frozen WRITE_ONCE(current->__state, TASK_FROZEN); ... /* Task is now marked frozen */ /* frozen(task) == true */ /* Assuming other tasks are frozen */ freezer->state |= CGROUP_FROZEN; /* freezing(current) returns false */ /* because cgroup is frozen (not freezing) */ break out __set_current_state(TASK_RUNNING); /* Bug: Task resumes running when it should remain frozen */ The existing !frozen(p) check in __thaw_task makes the WARN_ON_ONCE(freezing(p)) warning redundant. Removing this warning enables reverting the commit cff5f49d433f ("cgroup_freezer: cgroup_freezing: Check if not frozen") to resolve the issue. The warning has been removed in the previous patch. This patch revert the commit cff5f49d433f ("cgroup_freezer: cgroup_freezing: Check if not frozen") to complete the fix. Fixes: cff5f49d433f ("cgroup_freezer: cgroup_freezing: Check if not frozen") Reported-by: Zhong Jiaweizhongjiawei1@huawei.com Signed-off-by: Chen Ridong chenridong@huawei.com Signed-off-by: Tejun Heo tj@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org

diff --git a/kernel/cgroup/legacy_freezer.c b/kernel/cgroup/legacy_freezer.c index 507b8f19a262e..dd9417425d929 100644 --- a/kernel/cgroup/legacy_freezer.c +++ b/kernel/cgroup/legacy_freezer.c @@ -66,15 +66,9 @@ static struct freezer *parent_freezer(struct freezer *freezer) bool cgroup_freezing(struct task_struct *task) { bool ret;

• unsigned int state;

rcu_read_lock();

• /* 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);

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

return ret;