linux-kernel - [PATCH 4.2.y-ckt 165/218] sctp: fix the transports round robin issue when init is retransmitted

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Message-Id: <1459455431-12687-166-git-send-email-kamal@canonical.com>
Date:	Thu, 31 Mar 2016 13:16:18 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Xin Long <lucien.xin@...il.com>,
	"David S . Miller" <davem@...emloft.net>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 165/218] sctp: fix the transports round robin issue when init is retransmitted

4.2.8-ckt7 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Xin Long <lucien.xin@...il.com>

commit 39d2adebf137de5f900843f69f5e500932e31047 upstream.

prior to this patch, at the beginning if we have two paths in one assoc,
they may have the same params other than the last_time_heard, it will try
the paths like this:

1st cycle
  try trans1 fail.
  then trans2 is selected.(cause it's last_time_heard is after trans1).

2nd cycle:
  try  trans2 fail
  then trans2 is selected.(cause it's last_time_heard is after trans1).

3rd cycle:
  try  trans2 fail
  then trans2 is selected.(cause it's last_time_heard is after trans1).

....

trans1 will never have change to be selected, which is not what we expect.
we should keeping round robin all the paths if they are just added at the
beginning.

So at first every tranport's last_time_heard should be initialized 0, so
that we ensure they have the same value at the beginning, only by this,
all the transports could get equal chance to be selected.

Then for sctp_trans_elect_best, it should return the trans_next one when
*trans == *trans_next, so that we can try next if it fails,  but now it
always return trans. so we can fix it by exchanging these two params when
we calls sctp_trans_elect_tie().

Fixes: 4c47af4d5eb2 ('net: sctp: rework multihoming retransmission path selection to rfc4960')
Signed-off-by: Xin Long <lucien.xin@...il.com>
Acked-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 net/sctp/associola.c | 2 +-
 net/sctp/transport.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index 197c3f5..0f8e18f 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -1256,7 +1256,7 @@ static struct sctp_transport *sctp_trans_elect_best(struct sctp_transport *curr,
 	if (score_curr > score_best)
 		return curr;
 	else if (score_curr == score_best)
-		return sctp_trans_elect_tie(curr, best);
+		return sctp_trans_elect_tie(best, curr);
 	else
 		return best;
 }
diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index a0a4318..f45b05d 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -72,7 +72,7 @@ static struct sctp_transport *sctp_transport_init(struct net *net,
 	 */
 	peer->rto = msecs_to_jiffies(net->sctp.rto_initial);

-	peer->last_time_heard = ktime_get();
+	peer->last_time_heard = ktime_set(0, 0);
 	peer->last_time_ecne_reduced = jiffies;

 	peer->param_flags = SPP_HB_DISABLE |
-- 
2.7.4