[49/90] sch_sfq: fix sfq_enqueue()

[Greg KH]

3.0-stable review patch.  If anyone has any objections, please let us know.

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


From: Eric Dumazet <eric.dumazet@xxxxxxxxx>

[ Upstream commit e1738bd9cecc5c867b0e2996470c1ff20f66ba79 ]

commit 8efa88540635 (sch_sfq: avoid giving spurious NET_XMIT_CN signals)
forgot to call qdisc_tree_decrease_qlen() to signal upper levels that a
packet (from another flow) was dropped, leading to various problems.

With help from Michal Soltys and Michal Pokrywka, who did a bisection.

Bugzilla ref: https://bugzilla.kernel.org/show_bug.cgi?id=39372
Debian ref: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=631945

Reported-by: Lucas Bocchi <lucas.bocchi@xxxxxxxxx>
Reported-and-bisected-by: Michal Pokrywka <wolfmoon@xxxxx>
Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
CC: Michal Soltys <soltys@xxxxxxxx>
Acked-by: Patrick McHardy <kaber@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
---
 net/sched/sch_sfq.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/net/sched/sch_sfq.c
+++ b/net/sched/sch_sfq.c
@@ -410,7 +410,12 @@ sfq_enqueue(struct sk_buff *skb, struct
 	/* Return Congestion Notification only if we dropped a packet
 	 * from this flow.
 	 */
-	return (qlen != slot->qlen) ? NET_XMIT_CN : NET_XMIT_SUCCESS;
+	if (qlen != slot->qlen)
+		return NET_XMIT_CN;
+
+	/* As we dropped a packet, better let upper stack know this */
+	qdisc_tree_decrease_qlen(sch, 1);
+	return NET_XMIT_SUCCESS;
 }
 
 static struct sk_buff *


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