Messages in this thread | | | Date | Mon, 11 Mar 2013 16:37:42 -0700 | Subject | Re: epoll: possible bug from wakeup_source activation | From | Arve Hjønnevåg <> |
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On Fri, Mar 8, 2013 at 11:10 PM, Eric Wong <normalperson@yhbt.net> wrote: > Arve Hjønnevåg <arve@android.com> wrote: >> On Fri, Mar 8, 2013 at 12:49 PM, Eric Wong <normalperson@yhbt.net> 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-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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