Messages in this thread | | | Date | Thu, 25 Oct 2018 08:37:34 -0700 | From | Tejun Heo <> | Subject | Re: [PATCH 3/3] kernel/workqueue: Suppress a false positive lockdep complaint |
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On Thu, Oct 25, 2018 at 08:36:57AM -0700, Tejun Heo wrote: > Hello, Bart. > > On Thu, Oct 25, 2018 at 08:05:40AM -0700, Bart Van Assche wrote: > > diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h > > index 60d673e15632..375ec764f148 100644 > > --- a/include/linux/workqueue.h > > +++ b/include/linux/workqueue.h > > @@ -344,6 +344,7 @@ enum { > > __WQ_ORDERED = 1 << 17, /* internal: workqueue is ordered */ > > __WQ_LEGACY = 1 << 18, /* internal: create*_workqueue() */ > > __WQ_ORDERED_EXPLICIT = 1 << 19, /* internal: alloc_ordered_workqueue() */ > > + __WQ_HAS_BEEN_USED = 1 << 20, /* internal: work has been queued */ > > > > WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */ > > WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */ > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > > index fc9129d5909e..0ef275fe526c 100644 > > --- a/kernel/workqueue.c > > +++ b/kernel/workqueue.c > > @@ -1383,6 +1383,10 @@ static void __queue_work(int cpu, struct workqueue_struct *wq, > > if (unlikely(wq->flags & __WQ_DRAINING) && > > WARN_ON_ONCE(!is_chained_work(wq))) > > return; > > + > > + if (!(wq->flags & __WQ_HAS_BEEN_USED)) > > + wq->flags |= __WQ_HAS_BEEN_USED; > > + > > retry: > > if (req_cpu == WORK_CPU_UNBOUND) > > cpu = wq_select_unbound_cpu(raw_smp_processor_id()); > > @@ -2889,7 +2893,7 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr, > > * workqueues the deadlock happens when the rescuer stalls, blocking > > * forward progress. > > */ > > - if (!from_cancel && > > + if (!from_cancel && (pwq->wq->flags & __WQ_HAS_BEEN_USED) && > > (pwq->wq->saved_max_active == 1 || pwq->wq->rescuer)) { > > lock_acquire_exclusive(&pwq->wq->lockdep_map, 0, 0, NULL, > > _THIS_IP_); > > We likely wanna skip the whole drain instead of eliding lockdep > annotation here. Other than that, this patch looks fine to me but for > the others, I think it'd be a better idea to listen to Johannes. We > wanna annotate the users for the exceptions rather than weakening the > workqueue lockdep checks, especially because workqueue related > deadlocks can be pretty difficult to trigger and root cause > afterwards.
Ooh, also, please only do the HAS_BEEN_USED marking if LOCKDEP is enabled.
Thanks.
-- tejun
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