fs/epoll: avoid barrier after an epoll_wait(2) timeout

Upon timeout, we can just exit out of the loop, without the cost of the
changing the task's state with an smp_store_mb call.  Just exit out of
the loop and be done - setting the task state afterwards will be, of
course, redundant.

[dave@stgolabs.net: forgotten fixlets]
Link: http://lkml.kernel.org/r/20181109155258.jxcr4t2pnz6zqct3@linux-r8p5
Link: http://lkml.kernel.org/r/20181108051006.18751-7-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.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 b42f53d..9beb166 100644 (file)
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1820,15 +1820,19 @@ fetch_events:
                        res = -EINTR;
                        break;
                }
-               if (ep_events_available(ep) || timed_out)
+
+               eavail = ep_events_available(ep);
+               if (eavail)
                        break;
                if (signal_pending(current)) {
                        res = -EINTR;
                        break;
                }
 
-               if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
+               if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS)) {
                        timed_out = 1;
+                       break;
+               }
        }
 
        __set_current_state(TASK_RUNNING);