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@suse.de
Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 60f6b2712f5e9c539ed5d2a2972dbb2b7425b34e..53c3d4677dd4081a561611b7500948f5ed855454 100644 (file)
--- 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;
        }