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 20:31:33 -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 7:58 PM, John Fastabend
<john.fastabend@...il.com> wrote:
> On 12/18/2017 06:20 PM, Cong Wang wrote:
>> 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():
>>
>
> Except, the failed init path does not call qdisc_destroy.
>
> static struct Qdisc *qdisc_create(struct net_device *dev,
> [...]
>
>         if (ops->init) {
>                 err = ops->init(sch, tca[TCA_OPTIONS]);
>                 if (err != 0)
>                         goto err_out5;
>         }
> [...]
>
> err_out5:
>         /* ops->init() failed, we call ->destroy() like qdisc_create_dflt() */
>         if (ops->destroy)
>                 ops->destroy(sch);

Didn't I say qdisc_destroy() rather than ->destroy()? :-)


struct Qdisc *qdisc_create_dflt(struct netdev_queue *dev_queue,
                                const struct Qdisc_ops *ops,
                                unsigned int parentid)
{
        struct Qdisc *sch;

        if (!try_module_get(ops->owner))
                return NULL;

        sch = qdisc_alloc(dev_queue, ops);
        if (IS_ERR(sch)) {
                module_put(ops->owner);
                return NULL;
        }
        sch->parent = parentid;

        if (!ops->init || ops->init(sch, NULL) == 0)
                return sch;

        qdisc_destroy(sch);
        return NULL;
}