[PATCH] net_sched: prio: use qdisc_dequeue_peeked

[PATCH] net_sched: prio: use qdisc_dequeue_peeked

[Florian Westphal]

commit 07bd8df5df4369487812bf85a237322ff3569b77
(sch_sfq: fix peek() implementation) changed sfq to use generic
peek helper.

This makes HFSC complain about a non-work-conserving child qdisc, if
prio with sfq child is used within hfsc:

hfsc peeks into prio qdisc, which will then peek into sfq.
returned skb is stashed in sch->gso_skb.

Next, hfsc tries to dequeue from prio, but prio will call sfq dequeue
directly, which may return NULL instead of previously peeked-at skb.

Have prio call qdisc_dequeue_peeked, so sfq->dequeue() is
not called in this case.

Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 Eric, does this look correct to you?
 I am not sure if sfq needs fixing instead of this patch here.

diff --git a/net/sched/sch_prio.c b/net/sched/sch_prio.c
index 2a318f2..b5d56a2 100644
--- a/net/sched/sch_prio.c
+++ b/net/sched/sch_prio.c
@@ -112,7 +112,7 @@ static struct sk_buff *prio_dequeue(struct Qdisc *sch)
 
 	for (prio = 0; prio < q->bands; prio++) {
 		struct Qdisc *qdisc = q->queues[prio];
-		struct sk_buff *skb = qdisc->dequeue(qdisc);
+		struct sk_buff *skb = qdisc_dequeue_peeked(qdisc);
 		if (skb) {
 			qdisc_bstats_update(sch, skb);
 			sch->q.qlen--;
-- 
1.7.3.4

Re: [PATCH] net_sched: prio: use qdisc_dequeue_peeked

[Eric Dumazet]

Le mardi 09 août 2011 à 14:04 +0200, Florian Westphal a écrit :
> commit 07bd8df5df4369487812bf85a237322ff3569b77
> (sch_sfq: fix peek() implementation) changed sfq to use generic
> peek helper.
> 
> This makes HFSC complain about a non-work-conserving child qdisc, if
> prio with sfq child is used within hfsc:
> 
> hfsc peeks into prio qdisc, which will then peek into sfq.
> returned skb is stashed in sch->gso_skb.
> 
> Next, hfsc tries to dequeue from prio, but prio will call sfq dequeue
> directly, which may return NULL instead of previously peeked-at skb.
> 
> Have prio call qdisc_dequeue_peeked, so sfq->dequeue() is
> not called in this case.
> 
> Cc: Eric Dumazet <eric.dumazet@gmail.com>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
>  Eric, does this look correct to you?
>  I am not sure if sfq needs fixing instead of this patch here.
> 
> diff --git a/net/sched/sch_prio.c b/net/sched/sch_prio.c
> index 2a318f2..b5d56a2 100644
> --- a/net/sched/sch_prio.c
> +++ b/net/sched/sch_prio.c
> @@ -112,7 +112,7 @@ static struct sk_buff *prio_dequeue(struct Qdisc *sch)
>  
>  	for (prio = 0; prio < q->bands; prio++) {
>  		struct Qdisc *qdisc = q->queues[prio];
> -		struct sk_buff *skb = qdisc->dequeue(qdisc);
> +		struct sk_buff *skb = qdisc_dequeue_peeked(qdisc);
>  		if (skb) {
>  			qdisc_bstats_update(sch, skb);
>  			sch->q.qlen--;


Hi Florian

Are you sure this patch is still needed, after commit 
e1738bd9cecc5c867b0e2996470c1ff20f66ba79
(sch_sfq: fix sfq_enqueue())

I am asking before fully reviewing the code, I dont know who
should/shouldnt call qdisc_dequeue_peeked() instead of qdisc->dequeue()

Thanks !

Re: [PATCH] net_sched: prio: use qdisc_dequeue_peeked

[Florian Westphal]

Eric Dumazet <eric.dumazet@gmail.com> wrote:
> >  Eric, does this look correct to you?
> >  I am not sure if sfq needs fixing instead of this patch here.
> > 
> > diff --git a/net/sched/sch_prio.c b/net/sched/sch_prio.c
> > index 2a318f2..b5d56a2 100644
> > --- a/net/sched/sch_prio.c
> > +++ b/net/sched/sch_prio.c
> > @@ -112,7 +112,7 @@ static struct sk_buff *prio_dequeue(struct Qdisc *sch)
> >  
> >  	for (prio = 0; prio < q->bands; prio++) {
> >  		struct Qdisc *qdisc = q->queues[prio];
> > -		struct sk_buff *skb = qdisc->dequeue(qdisc);
> > +		struct sk_buff *skb = qdisc_dequeue_peeked(qdisc);
> >  		if (skb) {
> >  			qdisc_bstats_update(sch, skb);
> >  			sch->q.qlen--;
> 
> 
> Hi Florian
> 
> Are you sure this patch is still needed, after commit 
> e1738bd9cecc5c867b0e2996470c1ff20f66ba79
> (sch_sfq: fix sfq_enqueue())

Yes, I double checked.  This patch is applied, also
I see HFSC complaints even without that code path touched by
"sch_sfq: fix sfq_enqueue" being hit.

Re: [PATCH] net_sched: prio: use qdisc_dequeue_peeked

[David Miller]

From: Florian Westphal <fw@strlen.de>
Date: Tue,  9 Aug 2011 14:04:43 +0200

> commit 07bd8df5df4369487812bf85a237322ff3569b77
> (sch_sfq: fix peek() implementation) changed sfq to use generic
> peek helper.
> 
> This makes HFSC complain about a non-work-conserving child qdisc, if
> prio with sfq child is used within hfsc:
> 
> hfsc peeks into prio qdisc, which will then peek into sfq.
> returned skb is stashed in sch->gso_skb.
> 
> Next, hfsc tries to dequeue from prio, but prio will call sfq dequeue
> directly, which may return NULL instead of previously peeked-at skb.
> 
> Have prio call qdisc_dequeue_peeked, so sfq->dequeue() is
> not called in this case.
> 
> Cc: Eric Dumazet <eric.dumazet@gmail.com>
> Signed-off-by: Florian Westphal <fw@strlen.de>

Applied and queued up for -stable, thanks!