6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Chen Ridong chenridong@huawei.com
[ 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 --- 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 a3e13e6d5ee40..bee2f9ea5e4ae 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;