From: Elliot Berman Date: Mon, 20 Nov 2023 17:36:31 +0000 (-0800) Subject: freezer,sched: Do not restore saved_state of a thawed task X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=23ab79e8e469e2605beec2e3ccb40d19c68dd2e0;p=linux.git freezer,sched: Do not restore saved_state of a thawed task It is possible for a task to be thawed multiple times when mixing the *legacy* cgroup freezer and system-wide freezer. To do this, freeze the cgroup, do system-wide freeze/thaw, then thaw the cgroup. When this happens, then a stale saved_state can be written to the task's state and cause task to hang indefinitely. Fix this by only trying to thaw tasks that are actually frozen. This change also has the marginal benefit avoiding unnecessary wake_up_state(p, TASK_FROZEN) if we know the task is already thawed. There is not possibility of time-of-compare/time-of-use race when we skip the wake_up_state because entering/exiting TASK_FROZEN is guarded by freezer_lock. Fixes: 8f0eed4a78a8 ("freezer,sched: Use saved_state to reduce some spurious wakeups") Signed-off-by: Elliot Berman Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Abhijeet Dharmapurikar Link: https://lore.kernel.org/r/20231120-freezer-state-multiple-thaws-v1-1-f2e1dd7ce5a2@quicinc.com --- diff --git a/kernel/freezer.c b/kernel/freezer.c index c450fa8b8b5ef..759006a9a9102 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -201,7 +201,7 @@ void __thaw_task(struct task_struct *p) if (WARN_ON_ONCE(freezing(p))) goto unlock; - if (task_call_func(p, __restore_freezer_state, NULL)) + if (!frozen(p) || task_call_func(p, __restore_freezer_state, NULL)) goto unlock; wake_up_state(p, TASK_FROZEN);