sched,freezer: Remove unnecessary warning in __thaw_task

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@huawei.com>
Signed-off-by: Chen Ridong <chenridong@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/freezer.c b/kernel/freezer.c
index 8d530d0949ff69178edaf368222df847d026c842..6a96149aede9f59bfcee78376656bd4bb9914517 100644 (file)
--- 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);
 }
 
 /**