From 9beb8c5e77dc10e3889ff5f967eeffba78617a88 Mon Sep 17 00:00:00 2001 From: Chen Ridong Date: Thu, 17 Jul 2025 08:55:49 +0000 Subject: [PATCH 1/2] 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 Signed-off-by: Chen Ridong Signed-off-by: Tejun Heo --- 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); } /** From 14a67b42cb6f3ab66f41603c062c5056d32ea7dd Mon Sep 17 00:00:00 2001 From: Chen Ridong Date: Thu, 17 Jul 2025 08:55:50 +0000 Subject: [PATCH 2/2] Revert "cgroup_freezer: cgroup_freezing: Check if not frozen" 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 Jiawei Signed-off-by: Chen Ridong Signed-off-by: Tejun Heo --- kernel/cgroup/legacy_freezer.c | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-) diff --git a/kernel/cgroup/legacy_freezer.c b/kernel/cgroup/legacy_freezer.c index 507b8f19a262..dd9417425d92 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;