On 07/04, Johannes Berg wrote: > > On Tue, 2007-07-03 at 21:31 +0400, Oleg Nesterov wrote: > > > If A does NOT take a lock L1, then it is OK to do cancel_work_sync(A) > > under L1, regardless of which other work_structs this workqueue has, > > before or after A. > > Ah, cancel_work_sync() waits only for it if A is currently running? Yes. And no other work (except a barrier) can run before the caller of wait_on_work() is woken. > > Now we have a false positive if some time we queue B into that workqueue, > > and this is not good. > > Right. I was thinking of the flush_workqueue case where any of A or B > matters. Aha, now I see where I was confused. Yes, we can't avoid the false positives with flush_workqueue(). I hope this won't be a problem, because almost every usage of flush_workqueue() is pointless nowadays. So even if we have a false positive, it probably means the code needs cleanups anyway. But see below, > > We can avoid this problem if we put lockdep_map into work_struct, so > > that wait_on_work() "locks" work->lockdep_map, while flush_workqueue() > > takes wq->lockdep_map. > > Yeah, and then we'll take both wq->lockdep_map and the > work_struct->lockdep_map when running that work. That should work, I'll > give it a go later. If you are going to do this, may I suggest you to make 2 separate patches? Exactly because we can't avoid the false positives with flush_workqueue(), it would be nice if we have an option to revert the 2-nd patch if there are too many false positives (I hope this won't happen). (please ignore if this is not suitable for you). > > > @@ -257,7 +260,9 @@ static void run_workqueue(struct cpu_wor > > > > > > BUG_ON(get_wq_data(work) != cwq); > > > work_clear_pending(work); > > > + lock_acquire(&cwq->wq->lockdep_map, 0, 0, 0, 2, _THIS_IP_); > > > f(work); > > > + lock_release(&cwq->wq->lockdep_map, 0, _THIS_IP_); > > ^^^ > > Isn't it better to call lock_release() with nested == 1 ? > > Not sure, Ingo? Ingo, could you also explain the meaning of "nested" parameter? Looks like it is just unneeded, lock_release_nested() does a quick check and use lock_release_non_nested() when hlock is not on top of stack. Oleg. - To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
