linux-kernel - [ 037/120] pkt_sched: fix virtual-start-time update in QFQ

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Date:	Thu, 11 Oct 2012 09:59:49 +0900
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	alan@...rguk.ukuu.org.uk, Paolo Valente <paolo.valente@...more.it>,
	"David S. Miller" <davem@...emloft.net>
Subject: [ 037/120] pkt_sched: fix virtual-start-time update in QFQ

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

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

From: Paolo Valente <paolo.valente@...more.it>

[ Upstream commit 71261956973ba9e0637848a5adb4a5819b4bae83 ]

If the old timestamps of a class, say cl, are stale when the class
becomes active, then QFQ may assign to cl a much higher start time
than the maximum value allowed. This may happen when QFQ assigns to
the start time of cl the finish time of a group whose classes are
characterized by a higher value of the ratio
max_class_pkt/weight_of_the_class with respect to that of
cl. Inserting a class with a too high start time into the bucket list
corrupts the data structure and may eventually lead to crashes.
This patch limits the maximum start time assigned to a class.

Signed-off-by: Paolo Valente <paolo.valente@...more.it>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/sched/sch_qfq.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/net/sched/sch_qfq.c
+++ b/net/sched/sch_qfq.c
@@ -830,7 +830,10 @@ static void qfq_update_start(struct qfq_
 		if (mask) {
 			struct qfq_group *next = qfq_ffs(q, mask);
 			if (qfq_gt(roundedF, next->F)) {
-				cl->S = next->F;
+				if (qfq_gt(limit, next->F))
+					cl->S = next->F;
+				else /* preserve timestamp correctness */
+					cl->S = limit;
 				return;
 			}
 		}

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