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pkt_sched: sch_drr: fix drr_dequeue loop()

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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: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Patrick McHardy 2008-11-24 15:46:08 -08:00 committed by David S. Miller
parent 4b40eed73e
commit 3f0947c3ff
1 changed files with 5 additions and 3 deletions
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8
net/sched/sch_drr.c
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@ -373,11 +373,13 @@ static struct sk_buff *drr_dequeue(struct Qdisc *sch)
struct sk_buff *skb; struct sk_buff *skb;
unsigned int len; 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); cl = list_first_entry(&q->active, struct drr_class, alist);
skb = cl->qdisc->ops->peek(cl->qdisc); skb = cl->qdisc->ops->peek(cl->qdisc);
if (skb == NULL) if (skb == NULL)
goto skip; goto out;
len = qdisc_pkt_len(skb); len = qdisc_pkt_len(skb);
if (len <= cl->deficit) { if (len <= cl->deficit) {
@ -390,9 +392,9 @@ static struct sk_buff *drr_dequeue(struct Qdisc *sch)
} }
cl->deficit += cl->quantum; cl->deficit += cl->quantum;
skip:
list_move_tail(&cl->alist, &q->active); list_move_tail(&cl->alist, &q->active);
} }
out:
return NULL; return NULL;
} }