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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Ilya Dryomov <idryomov@gmail.com>,
        Jason Dillaman <dillaman@redhat.com>
Subject: [PATCH 4.16 087/113] libceph: reschedule a tick in finish_hunting()
Date:   Mon, 30 Apr 2018 12:24:58 -0700
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4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ilya Dryomov <idryomov@gmail.com>

commit 7b4c443d139f1d2b5570da475f7a9cbcef86740c upstream.

If we go without an established session for a while, backoff delay will
climb to 30 seconds.  The keepalive timeout is also 30 seconds, so it's
pretty easily hit after a prolonged hunting for a monitor: we don't get
a chance to send out a keepalive in time, which means we never get back
a keepalive ack in time, cutting an established session and attempting
to connect to a different monitor every 30 seconds:

  [Sun Apr 1 23:37:05 2018] libceph: mon0 10.80.20.99:6789 session established
  [Sun Apr 1 23:37:36 2018] libceph: mon0 10.80.20.99:6789 session lost, hunting for new mon
  [Sun Apr 1 23:37:36 2018] libceph: mon2 10.80.20.103:6789 session established
  [Sun Apr 1 23:38:07 2018] libceph: mon2 10.80.20.103:6789 session lost, hunting for new mon
  [Sun Apr 1 23:38:07 2018] libceph: mon1 10.80.20.100:6789 session established
  [Sun Apr 1 23:38:37 2018] libceph: mon1 10.80.20.100:6789 session lost, hunting for new mon
  [Sun Apr 1 23:38:37 2018] libceph: mon2 10.80.20.103:6789 session established
  [Sun Apr 1 23:39:08 2018] libceph: mon2 10.80.20.103:6789 session lost, hunting for new mon

The regular keepalive interval is 10 seconds.  After ->hunting is
cleared in finish_hunting(), call __schedule_delayed() to ensure we
send out a keepalive after 10 seconds.

Cc: stable@vger.kernel.org # 4.7+
Link: http://tracker.ceph.com/issues/23537
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Jason Dillaman <dillaman@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/ceph/mon_client.c |    1 +
 1 file changed, 1 insertion(+)

--- a/net/ceph/mon_client.c
+++ b/net/ceph/mon_client.c
@@ -1133,6 +1133,7 @@ static void finish_hunting(struct ceph_m
 		monc->hunting = false;
 		monc->had_a_connection = true;
 		un_backoff(monc);
+		__schedule_delayed(monc);
 	}
 }