Commit 3f0947c3 authored by Patrick McHardy's avatar Patrick McHardy Committed by David S. Miller

pkt_sched: sch_drr: fix drr_dequeue loop()

Jarek Poplawski points out:

If all child qdiscs of sch_drr are non-work-conserving (e.g. sch_tbf)
drr_dequeue() will busy-loop waiting for skbs instead of leaving the
job for a watchdog. Checking for list_empty() in each loop isn't
necessary either, because this can never be true except the first time.

Using non-work-conserving qdiscs as children of DRR makes no sense,
simply bail out in that case.
Reported-by: default avatarJarek Poplawski <>
Signed-off-by: default avatarPatrick McHardy <>
Signed-off-by: default avatarDavid S. Miller <>
parent 4b40eed7
......@@ -373,11 +373,13 @@ static struct sk_buff *drr_dequeue(struct Qdisc *sch)
struct sk_buff *skb;
unsigned int len;
while (!list_empty(&q->active)) {
if (list_empty(&q->active))
goto out;
while (1) {
cl = list_first_entry(&q->active, struct drr_class, alist);
skb = cl->qdisc->ops->peek(cl->qdisc);
if (skb == NULL)
goto skip;
goto out;
len = qdisc_pkt_len(skb);
if (len <= cl->deficit) {
......@@ -390,9 +392,9 @@ static struct sk_buff *drr_dequeue(struct Qdisc *sch)
cl->deficit += cl->quantum;
list_move_tail(&cl->alist, &q->active);
return NULL;
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