2016-04-12 06:46:07

by Lars Persson

Subject: [PATCH net v3] net: sched: do not requeue a NULL skb

A failure in validate_xmit_skb_list() triggered an unconditional call
to dev_requeue_skb with skb=NULL. This slowly grows the queue
discipline's qlen count until all traffic through the queue stops.

We take the optimistic approach and continue running the queue after a
failure since it is unknown if later packets also will fail in the
validate path.

Fixes: 55a93b3ea780 ("qdisc: validate skb without holding lock")
Signed-off-by: Lars Persson <[email protected]>
---
v3: After a discussion with Eric and Cong I went back to v1 and added the
likely() for the common path.
---
net/sched/sch_generic.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index f18c350..80742ed 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -159,12 +159,15 @@ int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
if (validate)
skb = validate_xmit_skb_list(skb, dev);

- if (skb) {
+ if (likely(skb)) {
HARD_TX_LOCK(dev, txq, smp_processor_id());
if (!netif_xmit_frozen_or_stopped(txq))
skb = dev_hard_start_xmit(skb, dev, txq, &ret);

HARD_TX_UNLOCK(dev, txq);
+ } else {
+ spin_lock(root_lock);
+ return qdisc_qlen(q);
}
spin_lock(root_lock);

--
2.1.4

2016-04-12 16:23:52

by Eric Dumazet

Subject: Re: [PATCH net v3] net: sched: do not requeue a NULL skb

On Tue, 2016-04-12 at 08:45 +0200, Lars Persson wrote:
> A failure in validate_xmit_skb_list() triggered an unconditional call
> to dev_requeue_skb with skb=NULL. This slowly grows the queue
> discipline's qlen count until all traffic through the queue stops.

>
> Fixes: 55a93b3ea780 ("qdisc: validate skb without holding lock")
> Signed-off-by: Lars Persson <[email protected]>
> ---


Acked-by: Eric Dumazet <[email protected]>

Thanks !

2016-04-14 05:29:35

by David Miller

Subject: Re: [PATCH net v3] net: sched: do not requeue a NULL skb

From: Lars Persson <[email protected]>
Date: Tue, 12 Apr 2016 08:45:52 +0200

> A failure in validate_xmit_skb_list() triggered an unconditional call
> to dev_requeue_skb with skb=NULL. This slowly grows the queue
> discipline's qlen count until all traffic through the queue stops.
>
> We take the optimistic approach and continue running the queue after a
> failure since it is unknown if later packets also will fail in the
> validate path.
>
> Fixes: 55a93b3ea780 ("qdisc: validate skb without holding lock")
> Signed-off-by: Lars Persson <[email protected]>

Applied and queued up for -stable, thanks.