From abc610e01c663e25c41a3bdcbc4115cd7fbb047b Mon Sep 17 00:00:00 2001
From: Davidlohr Bueso <dave@stgolabs.net>
Date: Thu, 3 Jan 2019 15:27:19 -0800
Subject: [PATCH] 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>
---
fs/eventpoll.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index b42f53d64d11b..9beb166b7264a 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1820,15 +1820,19 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *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);
--
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