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    SubjectRe: [PATCH UPDATED] workqueue: relax lockdep annotation on flush_work()
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    On Mon, 2011-01-03 at 16:00 +0100, Tejun Heo wrote:
    > Hello,
    >
    > On Mon, Jan 03, 2011 at 03:54:50PM +0100, Peter Zijlstra wrote:
    > > On Mon, 2011-01-03 at 15:17 +0100, Tejun Heo wrote:
    > >
    > > > @@ -2384,8 +2384,18 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
    > > > insert_wq_barrier(cwq, barr, work, worker);
    > > > spin_unlock_irq(&gcwq->lock);
    > > >
    > > > - lock_map_acquire(&cwq->wq->lockdep_map);
    > > > + /*
    > > > + * If @max_active is 1 or rescuer is in use, flushing another work
    > > > + * item on the same workqueue may lead to deadlock. Make sure the
    > > > + * flusher is not running on the same workqueue by verifying write
    > > > + * access.
    > > > + */
    > > > + if (cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER)
    > > > + lock_map_acquire(&cwq->wq->lockdep_map);
    > > > + else
    > > > + lock_map_acquire_read(&cwq->wq->lockdep_map);
    > > > lock_map_release(&cwq->wq->lockdep_map);
    > > > +
    > > > return true;
    > > > already_gone:
    > > > spin_unlock_irq(&gcwq->lock);
    > >
    > > Ah, but this violates the rule that you must always use the most strict
    > > constraints. Code doesn't know if it will run in a rescue thread or not,
    > > hence it must assume it does.
    >
    > Hmmm? The code applies the most strict contraints. If the workqueue
    > has a rescuer, flushing another work from the workqueue will always
    > trigger lockdep warning. The rule is relaxed only for workqueues
    > which aren't used for memory reclaiming && support parallel execution.

    Ah, ok. I read it like: if the current thread is a rescue thread.




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