netdev - Re: [Patch net-next] net_sched: properly check for empty skb array on error path

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Date:   Mon, 18 Dec 2017 18:20:07 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [Patch net-next] net_sched: properly check for empty skb array on
 error path

On Mon, Dec 18, 2017 at 5:25 PM, John Fastabend
<john.fastabend@...il.com> wrote:
> On 12/18/2017 02:34 PM, Cong Wang wrote:
>> First, the check of &q->ring.queue against NULL is wrong, it
>> is always false. We should check the value rather than the address.
>>
>
> Thanks.
>
>> Secondly, we need the same check in pfifo_fast_reset() too,
>> as both ->reset() and ->destroy() are called in qdisc_destroy().
>>
>
> not that it hurts to have the check here, but if init fails
> in qdisc_create it seems only ->destroy() is called without
> a ->reset().
>
> Is there another path for init() to fail that I'm missing.

Pretty sure ->reset() is called in qdisc_destroy() and also before
->destroy():


void qdisc_destroy(struct Qdisc *qdisc)
{
        const struct Qdisc_ops  *ops = qdisc->ops;
        struct sk_buff *skb, *tmp;

        if (qdisc->flags & TCQ_F_BUILTIN ||
            !refcount_dec_and_test(&qdisc->refcnt))
                return;

#ifdef CONFIG_NET_SCHED
        qdisc_hash_del(qdisc);

        qdisc_put_stab(rtnl_dereference(qdisc->stab));
#endif
        gen_kill_estimator(&qdisc->rate_est);
        if (ops->reset)
                ops->reset(qdisc);
        if (ops->destroy)
                ops->destroy(qdisc);