netdev - Re: [Bugme-new] [Bug 39372] New: Problems with HFSC Scheduler

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Date:	Sat, 30 Jul 2011 07:22:42 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Patrick McHardy <kaber@...sh.net>,
	David Miller <davem@...emloft.net>
Cc:	Michal Soltys <soltys@....info>,
	Andrew Morton <akpm@...ux-foundation.org>,
	netdev@...r.kernel.org, bugme-daemon@...zilla.kernel.org,
	Jamal Hadi Salim <hadi@...erus.ca>, lucas.bocchi@...il.com,
	631945@...s.debian.org, 00bormoj@...il.com,
	fdelawarde@...elessmundi.com
Subject: Re: [Bugme-new] [Bug 39372] New: Problems with HFSC Scheduler

Le vendredi 29 juillet 2011 à 16:11 +0200, Patrick McHardy a écrit :

> Yeah, that seems to be the correct fix, thanks for looking into this.

Thanks Patrick, here is the official patch submission then ;)

[PATCH] sch_sfq: fix sfq_enqueue()

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@...il.com>
Reported-and-bisected-by: Michal Pokrywka <wolfmoon@...pl>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
CC: Michal Soltys <soltys@....info>
Acked-by: Patrick McHardy <kaber@...sh.net>
---
 net/sched/sch_sfq.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
index 4536ee6..2a2d287 100644
--- a/net/sched/sch_sfq.c
+++ b/net/sched/sch_sfq.c
@@ -410,7 +410,12 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 	/* 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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