From: Roman Penyaev <rpenyaev@xxxxxxx> Subject: epoll: unify awaking of wakeup source on ep_poll_callback() path Original comment "Activate ep->ws since epi->ws may get deactivated at any time" indeed sounds loud, but it is incorrect, because the path where we check epi->ws is a path where insert to ovflist happens, i.e. ep_scan_ready_list() has taken ep->mtx and waits for this callback to finish, thus ep_modify() (which unregisters wakeup source) waits for ep_scan_ready_list(). Here in this patch I simply call ep_pm_stay_awake_rcu(), which is a bit extra for this path (indirectly protected by main ep->mtx, so even rcu is not needed), but I do not want to create another naked __ep_pm_stay_awake() variant only for this particular case, so rcu variant is just better for all the cases. Link: http://lkml.kernel.org/r/20190103150104.17128-4-rpenyaev@xxxxxxx Signed-off-by: Roman Penyaev <rpenyaev@xxxxxxx> Cc: Davidlohr Bueso <dbueso@xxxxxxx> Cc: Jason Baron <jbaron@xxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/fs/eventpoll.c~epoll-unify-awaking-of-wakeup-source-on-ep_poll_callback-path +++ a/fs/eventpoll.c @@ -1162,14 +1162,7 @@ static int ep_poll_callback(wait_queue_e if (epi->next == EP_UNACTIVE_PTR) { epi->next = READ_ONCE(ep->ovflist); WRITE_ONCE(ep->ovflist, epi); - if (epi->ws) { - /* - * Activate ep->ws since epi->ws may get - * deactivated at any time. - */ - __pm_stay_awake(ep->ws); - } - + ep_pm_stay_awake_rcu(epi); } goto out_unlock; } _
