linux-kernel - [PATCH] epoll: preserve ordering of events from ovflist

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Date:	Sat, 2 Mar 2013 07:25:08 +0000
From:	Eric Wong <normalperson@...t.net>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] epoll: preserve ordering of events from ovflist

Events arriving in ovflist are stored in LIFO order, so
we should account for that when inserting them into rddlist.

Signed-off-by: Eric Wong <normalperson@...t.net>
Cc: Davide Libenzi <davidel@...ilserver.org>
Cc: Al Viro <viro@...IV.linux.org.uk>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---
  I think this can lead to starvation in some rare cases, but I have not
  been able to trigger it.  The window for ovflist insertion is tiny.

 fs/eventpoll.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 9fec183..5a1a596 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -598,7 +598,7 @@ static int ep_scan_ready_list(struct eventpoll *ep,
 		 * contain them, and the list_splice() below takes care of them.
 		 */
 		if (!ep_is_linked(&epi->rdllink)) {
-			list_add_tail(&epi->rdllink, &ep->rdllist);
+			list_add(&epi->rdllink, &ep->rdllist);
 			__pm_stay_awake(epi->ws);
 		}
 	}
-- 
Eric Wong
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