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Revert "cgroup_freezer: cgroup_freezing: Check if not frozen"

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[ Upstream commit 14a67b42cb ]

This reverts commit cff5f49d43.

Commit cff5f49d43 ("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 cff5f49d43 ("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 cff5f49d43 ("cgroup_freezer: cgroup_freezing: Check if not
frozen") to complete the fix.

Fixes: cff5f49d43 ("cgroup_freezer: cgroup_freezing: Check if not frozen")
Reported-by: Zhong Jiawei<zhongjiawei1@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>
This commit is contained in:
Chen Ridong 2025-07-17 08:55:50 +00:00 committed by Greg Kroah-Hartman
parent 74bb4de32d
commit f371ad6471
1 changed files with 1 additions and 7 deletions
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8
kernel/cgroup/legacy_freezer.c
View File

@ -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;