Messages in this thread Patch in this message | | | Subject | Re: [PATCH] kthread/smpboot: Serialize kthread parking against wakeup | From | "Kohli, Gaurav" <> | Date | Tue, 24 Apr 2018 20:12:49 +0530 |
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Hi ,
We can also fix below race by smpboot code as well:
@@ -109,7 +109,6 @@ static int smpboot_thread_fn(void *data)
struct smp_hotplug_thread *ht = td->ht;
while (1) {
- set_current_state(TASK_INTERRUPTIBLE);
preempt_disable();
if (kthread_should_stop()) {
__set_current_state(TASK_RUNNING);
@@ -157,6 +156,7 @@ static int smpboot_thread_fn(void *data)
if (!ht->thread_should_run(td->cpu)) {
preempt_enable_no_resched();
+ set_current_state(TASK_INTERRUPTIBLE);
schedule(); } else { __set_current_state(TASK_RUNNING);
Please suggest if this approach is better.
Regards
Gaurav
On 4/24/2018 2:58 PM, Gaurav Kohli wrote:
> 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()); > -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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