# \[PATCH net\] pkt\_sched: fq: avoid hang when quantum 0

- From: Kenneth Klette Jonassen \<hidden\>
- Date: 2015-02-03 16:50:16 
- List: netdev
- Page: https://ratatoskr.run/netdev/2015/02/10977115
- Thread: https://ratatoskr.run/netdev/2015/02/10977115/t.md

```text
Configuring fq with quantum 0 hangs the system, presumably because of a
non-interruptible infinite loop. Either way quantum 0 does not make sense.

Reproduce with:
sudo tc qdisc add dev lo root fq quantum 0 initial_quantum 0
ping 127.0.0.1

Signed-off-by: Kenneth Klette Jonassen <redacted>
---
 net/sched/sch_fq.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c
index 2a50f5c..313794b 100644
--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -670,8 +670,14 @@ static int fq_change(struct Qdisc *sch, struct nlattr *opt)
 	if (tb[TCA_FQ_FLOW_PLIMIT])
 		q->flow_plimit = nla_get_u32(tb[TCA_FQ_FLOW_PLIMIT]);
 
-	if (tb[TCA_FQ_QUANTUM])
-		q->quantum = nla_get_u32(tb[TCA_FQ_QUANTUM]);
+	if (tb[TCA_FQ_QUANTUM]) {
+		u32 quantum = nla_get_u32(tb[TCA_FQ_QUANTUM]);
+
+		if (quantum > 0)
+			q->quantum = quantum;
+		else
+			err = -EINVAL;
+	}
 
 	if (tb[TCA_FQ_INITIAL_QUANTUM])
 		q->initial_quantum = nla_get_u32(tb[TCA_FQ_INITIAL_QUANTUM]);
-- 
1.9.1
```