linux-kernel - [PATCH v2 -next 1/2] sched,freezer: Remove unnecessary warning in __thaw

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Message-Id: <20250717085550.3828781-2-chenridong@huaweicloud.com>
Date: Thu, 17 Jul 2025 08:55:49 +0000
From: Chen Ridong <chenridong@...weicloud.com>
To: tj@...nel.org,
	hannes@...xchg.org,
	mkoutny@...e.com,
	rafael@...nel.org,
	pavel@...nel.org,
	timvp@...gle.com
Cc: cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org,
	lujialin4@...wei.com,
	chenridong@...wei.com
Subject: [PATCH v2 -next 1/2] sched,freezer: Remove unnecessary warning in __thaw_task

From: Chen Ridong <chenridong@...wei.com>

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 commit cff5f49d433f ("cgroup_freezer: cgroup_freezing: Check if
not frozen") to resolve the issue.

This patch removes the warning from __thaw_task. A subsequent patch will
revert commit cff5f49d433f ("cgroup_freezer: cgroup_freezing: Check if
not frozen") to complete the fix.

Reported-by: Zhong Jiawei<zhongjiawei1@...wei.com>
Signed-off-by: Chen Ridong <chenridong@...wei.com>
---
 kernel/freezer.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/kernel/freezer.c b/kernel/freezer.c
index 8d530d0949ff..6a96149aede9 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -201,18 +201,9 @@ static int __restore_freezer_state(struct task_struct *p, void *arg)
 
 void __thaw_task(struct task_struct *p)
 {
-	unsigned long flags;
-
-	spin_lock_irqsave(&freezer_lock, flags);
-	if (WARN_ON_ONCE(freezing(p)))
-		goto unlock;
-
-	if (!frozen(p) || task_call_func(p, __restore_freezer_state, NULL))
-		goto unlock;
-
-	wake_up_state(p, TASK_FROZEN);
-unlock:
-	spin_unlock_irqrestore(&freezer_lock, flags);
+	guard(spinlock_irqsave)(&freezer_lock);
+	if (frozen(p) && !task_call_func(p, __restore_freezer_state, NULL))
+		wake_up_state(p, TASK_FROZEN);
 }
 
 /**
-- 
2.34.1