Messages in this thread | | | Subject | Re: [PATCH v2] psi: get poll_work to run when calling poll syscall next time | From | Jason Xing <> | Date | Fri, 2 Aug 2019 14:20:26 +0800 |
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Hi all,
According to the reviews from Johoannes, I've changed the old patch and then submitted the version 2 patch a few days ago.
Please let me know if all this sounds good, or if there are any issues.
Thanks, Jason
On 2019/7/30 下午1:16, Jason Xing wrote: > Only when calling the poll syscall the first time can user > receive POLLPRI correctly. After that, user always fails to > acquire the event signal. > > Reproduce case: > 1. Get the monitor code in Documentation/accounting/psi.txt > 2. Run it, and wait for the event triggered. > 3. Kill and restart the process. > > If the user doesn't kill the monitor process, it seems the > poll_work works fine. After killing and restarting the monitor, > the poll_work in kernel will never run again due to the wrong > value of poll_scheduled. Therefore, we should reset the value > as group_init() does after the last trigger is destroyed. > > [PATCH V2] > In the patch v2, I put the atomic_set(&group->poll_scheduled, 0); > into the right place. > Here I quoted from Johannes as the best explaination: > "The question is why we can end up with poll_scheduled = 1 but the work > not running (which would reset it to 0). And the answer is because the > scheduling side sees group->poll_kworker under RCU protection and then > schedules it, but here we cancel the work and destroy the worker. The > cancel needs to pair with resetting the poll_scheduled flag." > > Signed-off-by: Jason Xing <kerneljasonxing@linux.alibaba.com> > Reviewed-by: Caspar Zhang <caspar@linux.alibaba.com> > Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com> > Reviewed-by: Suren Baghdasaryan <surenb@google.com> > Acked-by: Johannes Weiner <hannes@cmpxchg.org> > --- > kernel/sched/psi.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c > index 7acc632..acdada0 100644 > --- a/kernel/sched/psi.c > +++ b/kernel/sched/psi.c > @@ -1131,7 +1131,14 @@ static void psi_trigger_destroy(struct kref *ref) > * deadlock while waiting for psi_poll_work to acquire trigger_lock > */ > if (kworker_to_destroy) { > + /* > + * After the RCU grace period has expired, the worker > + * can no longer be found through group->poll_kworker. > + * But it might have been already scheduled before > + * that - deschedule it cleanly before destroying it. > + */ > kthread_cancel_delayed_work_sync(&group->poll_work); > + atomic_set(&group->poll_scheduled, 0); > kthread_destroy_worker(kworker_to_destroy); > } > kfree(t); >
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