Messages in this thread Patch in this message | | | From | Gaurav Kohli <> | Subject | [PATCH] kthread/smpboot: Serialize kthread parking against wakeup | Date | Tue, 24 Apr 2018 14:58:25 +0530 |
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The control cpu thread which initiates hotplug calls kthread_park() for hotplug thread and sets KTHREAD_SHOULD_PARK. After this control thread wakes up the hotplug thread. There is a chance that wakeup code sees the hotplug thread (running on AP core) in INTERRUPTIBLE state, but sets its state to RUNNING after hotplug thread has entered kthread_parkme() and changed its state to TASK_PARKED. This can result in panic later on in kthread_unpark(), as it sees KTHREAD_IS_PARKED flag set but fails to rebind the kthread, due to it being not in TASK_PARKED state. Fix this, by serializing wakeup state change, against state change before parking the kthread.
Below is the possible race:
Control thread Hotplug Thread
kthread_park() set KTHREAD_SHOULD_PARK smpboot_thread_fn set_current_state(TASK_INTERRUPTIBLE); kthread_parkme
wake_up_process()
raw_spin_lock_irqsave(&p->pi_lock, flags); if (!(p->state & state)) -> this will fail goto out;
__kthread_parkme __set_current_state(TASK_PARKED);
if (p->on_rq && ttwu_remote(p, wake_flags)) ttwu_remote() p->state = TASK_RUNNING; schedule();
So to avoid this race, take pi_lock to serial state changes.
Suggested-by: Pavankumar Kondeti <pkondeti@codeaurora.org> Co-developed-by: Neeraj Upadhyay <neeraju@codeaurora.org> Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> Signed-off-by: Gaurav Kohli <gkohli@codeaurora.org>
diff --git a/kernel/smpboot.c b/kernel/smpboot.c index 1650578..514b232 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -121,7 +121,9 @@ static int smpboot_thread_fn(void *data) } if (kthread_should_park()) { + raw_spin_lock(¤t->pi_lock); __set_current_state(TASK_RUNNING); + raw_spin_unlock(¤t->pi_lock); preempt_enable(); if (ht->park && td->status == HP_THREAD_ACTIVE) { BUG_ON(td->cpu != smp_processor_id()); -- 1.9.1
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