[v2,1/4] epoll: make sure all elements in ready list are in FIFO order
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Message ID 20190103150104.17128-2-rpenyaev@suse.de
State In Next
Commit e89d04c816431202b27d312847df8ca84b1d298f
Headers show
  • use rwlock in order to reduce ep_poll_callback() contention
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Commit Message

Roman Penyaev Jan. 3, 2019, 3:01 p.m. UTC
All coming events are stored in FIFO order and this is also should be
applicable to ->ovflist, which originally is stack, i.e. LIFO.

Thus to keep correct FIFO order ->ovflist should reversed by adding
elements to the head of the read list but not to the tail.

Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
 fs/eventpoll.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

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diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 2329f96469e2..3627c2e07149 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -722,7 +722,11 @@  static __poll_t ep_scan_ready_list(struct eventpoll *ep,
 		 * contain them, and the list_splice() below takes care of them.
 		if (!ep_is_linked(epi)) {
-			list_add_tail(&epi->rdllink, &ep->rdllist);
+			/*
+			 * ->ovflist is LIFO, so we have to reverse it in order
+			 * to keep in FIFO.
+			 */
+			list_add(&epi->rdllink, &ep->rdllist);