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SubjectRe: [PATCH net v2] net: sched: do not requeue a NULL skb


On 04/11/2016 03:23 PM, Eric Dumazet wrote:
> On Mon, 2016-04-11 at 08:24 +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.
>>
>> By introducing a NULL check in dev_requeue_skb it was also necessary
>> to make the __netif_schedule call conditional to avoid scheduling an
>> empty queue.
>>
>> Fixes: 55a93b3ea780 ("qdisc: validate skb without holding lock")
>> Signed-off-by: Lars Persson <larper@axis.com>
>> ---
>> net/sched/sch_generic.c | 11 +++++++----
>> 1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
>> index f18c350..4e6a79c 100644
>> --- a/net/sched/sch_generic.c
>> +++ b/net/sched/sch_generic.c
>> @@ -47,10 +47,13 @@ EXPORT_SYMBOL(default_qdisc_ops);
>>
>> static inline int dev_requeue_skb(struct sk_buff *skb, struct Qdisc *q)
>> {
>> - q->gso_skb = skb;
>> - q->qstats.requeues++;
>> - q->q.qlen++; /* it's still part of the queue */
>> - __netif_schedule(q);
>> + if (skb) {
>> + q->gso_skb = skb;
>> + q->qstats.requeues++;
>> + q->q.qlen++; /* it's still part of the queue */
>> + }
>> + if (qdisc_qlen(q))
>> + __netif_schedule(q);
>>
>> return 0;
>> }
>
>
> Please always CC patch author when fixing a bug.
>
> Why adding the if (qdisc_qlen(q)) extra test ?
>
> This seems unrelated to the bug fix, and probably should be part of a
> second patch targeting net-next tree.

I though it would be prudent because the queue can be non-empty even for
the case of skb=NULL. So should it be there in this patch, another patch
or not at all ?

>
> Also please add a likely() clause
>
> if (likely(skb)) {
> q->gso_skb = skb;
> q->qstats.requeues++;
> q->q.qlen++; /* it's still part of the queue */
> __netif_schedule(q);
> }

Will fix.

> Thanks !
>
>
>
>
>

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