netdev - [PATCH] sch_qfq: fix overflow in qfq_update

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Date:	Mon, 02 Jan 2012 16:47:57 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>,
	Stephen Hemminger <shemminger@...tta.com>,
	Dave Taht <dave.taht@...il.com>
Subject: [PATCH] sch_qfq: fix overflow in qfq_update_start()

grp->slot_shift is between 22 and 41, so using 32bit wide variables is
probably a typo.

This could explain QFQ hangs Dave reported to me, after 2^23 packets ?

(23 = 64 - 41)

Reported-by: Dave Taht <dave.taht@...il.com>
CC: Stephen Hemminger <shemminger@...tta.com>
CC: Dave Taht <dave.taht@...il.com>
---
 net/sched/sch_qfq.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c
index 1033434..7b03254 100644
--- a/net/sched/sch_qfq.c
+++ b/net/sched/sch_qfq.c
@@ -817,11 +817,11 @@ skip_unblock:
 static void qfq_update_start(struct qfq_sched *q, struct qfq_class *cl)
 {
 	unsigned long mask;
-	uint32_t limit, roundedF;
+	u64 limit, roundedF;
 	int slot_shift = cl->grp->slot_shift;
 
 	roundedF = qfq_round_down(cl->F, slot_shift);
-	limit = qfq_round_down(q->V, slot_shift) + (1UL << slot_shift);
+	limit = qfq_round_down(q->V, slot_shift) + (1ULL << slot_shift);
 
 	if (!qfq_gt(cl->F, q->V) || qfq_gt(roundedF, limit)) {
 		/* timestamp was stale */


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