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FROMGIT: freezer,sched: do not restore saved_state of a thawed task

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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 <quic_eberman@quicinc.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Abhijeet Dharmapurikar <quic_adharmap@quicinc.com>
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 <fengqi@xiaomi.corp-partner.google.com>
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
This commit is contained in:
Elliot Berman 2023-11-20 09:36:31 -08:00 • committed by William McVicker
parent 6e3127c7ba
commit 2a5c5d7c47
1 changed files with 1 additions and 1 deletions
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2
kernel/freezer.c
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@ -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);