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/[email protected]
Signed-off-by: Roman Penyaev <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Jason Baron <[email protected]>
Cc: Al Viro <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 1 insertions, 8 deletions

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 60f6b2712f5e..53c3d4677dd4 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1162,14 +1162,7 @@ static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, v
 		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;
 	}