On Sun, Aug 30, 2009 at 10:05:59PM -0700, David Miller wrote:

From: Jarek Poplawski <redacted>
Date: Wed, 26 Aug 2009 23:59:56 +0200

quoted

Denys Fedoryschenko wrote, On 08/25/2009 02:18 PM:
...

quoted

Just maybe good idea in next kernels to document this or handle overflow, that 
it will give warning in kernel. Otherwise user will have non-functional qdisc 
that will not pass traffic.

OK, if this patch works for you send your Tested-by, please.

Denys, please give Jarek's patch some testing and let us know
if it triggers properly for you.

Actually, I think now, after 2.6.31, this patch might be a bit too
late. If people hit this problem they probably should've fixed it
until -next already, so let's forget about this patch until there are
more such reports.

Btw, I guess, Denys could submit some warnings into iproute's code
and/or documentation, as he proposed earlier.

Thanks,
Jarek P.

quoted

---------------->
pkt_sched: Warn on tokens overflow in tbf_dequeue

After recent change of scheduling resolution some "extreme" configs
can cause token overflows with stalls. This patch warns when tokens
were negative before accounting for a packet length.

Reported-by: Denys Fedoryschenko <redacted>
Signed-off-by: Jarek Poplawski <redacted>
---

 net/sched/sch_tbf.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
index e22dfe8..ef191c4 100644
--- a/net/sched/sch_tbf.c
+++ b/net/sched/sch_tbf.c

@@ -191,6 +191,12 @@ static struct sk_buff *tbf_dequeue(struct Qdisc* sch)
 			return skb;
 		}
 
+		if (unlikely((long)(toks + L2T(q, len)) < 0 ||
+			     (long)(ptoks + L2T_P(q, len) < 0)))
+			if (net_ratelimit())
+				pr_warning("tbf: tokens overflow;"
+					   " fix limits.\n");
+
 		qdisc_watchdog_schedule(&q->watchdog,
 					now + max_t(long, -toks, -ptoks));
 
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