From 2a5c5d7c47d52558eeb1c44afc68caa48cb719ad Mon Sep 17 00:00:00 2001 From: Elliot Berman Date: Mon, 20 Nov 2023 09:36:31 -0800 Subject: [PATCH] FROMGIT: 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 Bug: 292064955 Bug: 312992017 (cherry picked from commit 23ab79e8e469e2605beec2e3ccb40d19c68dd2e0 https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched/urgent) Change-Id: I09cb09a3ef3641c71e3b3156bc3a9a3e69d4966e Signed-off-by: Qi Feng Signed-off-by: Elliot Berman --- kernel/freezer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/freezer.c b/kernel/freezer.c index abd7f58cfe04..c5092209c609 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -205,7 +205,7 @@ 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);