On Fri, Mar 8, 2013 at 11:10 PM, Eric Wong <normalperson@xxxxxxxx> wrote: > Arve Hjønnevåg <arve@xxxxxxxxxxx> wrote: >> On Fri, Mar 8, 2013 at 12:49 PM, Eric Wong <normalperson@xxxxxxxx> wrote: >> > What happens if ep_modify calls ep_destroy_wakeup_source >> > while __pm_stay_awake is running on the same epi->ws? >> >> Yes, that looks like a problem. I think calling >> ep_destroy_wakeup_source with ep->lock held should fix that. It is not >> clear how useful changing EPOLLWAKEUP in ep_modify is, so >> alternatively we could remove that feature and instead only allow it >> to be set in ep_insert. > > ep->lock would work, but ep->lock is already a source of heavy > contention in my multithreaded+epoll webservers. > This should not have any significant impact on that since you would be adding a lock to a code path that is, as far as I know, unused. > Perhaps RCU can be used? I've no experience with RCU, but I've been > meaning to get acquainted with RCU. > That adds code to the common path however. The wakeup_source is not touch without holding one of the locks so holding both locks before deleting it seems like a simpler solution. > Another possible solution is to only use ep->ws and add an atomic > counter to ep; so __pm_relax(ep->ws) is only called when the atomic > counter reaches zero. -- Arve Hjønnevåg -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
