From: Chen Ridong <[email protected]>
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<[email protected]>
Signed-off-by: Chen Ridong <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>
https://virtuozzo.atlassian.net/browse/VSTOR-118578
(cherry picked from commit 14a67b42cb6f3ab66f41603c062c5056d32ea7dd)
Signed-off-by: Pavel Tikhomirov <[email protected]>
Feature: cgroup/freeze: improvements
---
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 10b643dd570db..b048f6b530688 100644
--- a/kernel/cgroup/legacy_freezer.c
+++ b/kernel/cgroup/legacy_freezer.c
@@ -71,15 +71,9 @@ 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;
--
2.51.1
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