Subject: Re: [PATCH net] net/sched: fix netdevice reference leaks in attach_one_default_qdisc()

From: "wanghai (M)" <[email-masked]>
Date: Thu, 25 Aug 2022 20:29:21 +0800

在 2022/8/19 23:58, wanghai (M) 写道:
>
> 在 2022/8/19 1:56, Jakub Kicinski 写道:
>> On Wed, 17 Aug 2022 18:46:46 +0800 Wang Hai wrote:
>>> In attach_default_qdiscs(), when attach default qdisc (fq_codel) fails
>>> and fallback to noqueue, if the original attached qdisc is not released
>>> and a new one is directly attached, this will cause netdevice reference
>>> leaks.
>> Could you provide more details on the failure path? My preference would
>> be to try to clean up properly there, if possible.
> Hi Jakub.
>
> Here are the details of the failure. Do I need to do cleanup under the 
> failed path?
>
> If a dev has multiple queues and queue 0 fails to attach qdisc
> because there is no memory in attach_one_default_qdisc(). Then
> dev->qdisc will be noop_qdisc by default. But the other queues
> may be able to successfully attach to default qdisc.
>
> In this case, the fallback to noqueue process will be triggered
>
> static void attach_default_qdiscs(struct net_device *dev)
> {
>     ...
>     if (!netif_is_multiqueue(dev) ||
>         dev->priv_flags & IFF_NO_QUEUE) {
>             ...
>             netdev_for_each_tx_queue(dev, attach_one_default_qdisc, 
> NULL); // queue 0 attach failed because -ENOBUFS, but the other queues 
> attach successfully
>             qdisc = txq->qdisc_sleeping;
>             rcu_assign_pointer(dev->qdisc, qdisc); // dev->qdisc = 
> &noop_qdisc
>             ...
>     }
>     ...
>     if (qdisc == &noop_qdisc) {
>         ...
>         netdev_for_each_tx_queue(dev, attach_one_default_qdisc, NULL); 
> // Re-attach, but not release the previously created qdisc
>         ...
>     }
> }
>
Hi Jakub.
Do you have any other suggestions for this patch? Any replies would be 
appreciated.

>>> The following is the bug log:
>>>
>>> veth0: default qdisc (fq_codel) fail, fallback to noqueue
>>> unregister_netdevice: waiting for veth0 to become free. Usage count 
>>> = 32
>>> leaked reference.
>>>   qdisc_alloc+0x12e/0x210
>>>   qdisc_create_dflt+0x62/0x140
>>>   attach_one_default_qdisc.constprop.41+0x44/0x70
>>>   dev_activate+0x128/0x290
>>>   __dev_open+0x12a/0x190
>>>   __dev_change_flags+0x1a2/0x1f0
>>>   dev_change_flags+0x23/0x60
>>>   do_setlink+0x332/0x1150
>>>   __rtnl_newlink+0x52f/0x8e0
>>>   rtnl_newlink+0x43/0x70
>>>   rtnetlink_rcv_msg+0x140/0x3b0
>>>   netlink_rcv_skb+0x50/0x100
>>>   netlink_unicast+0x1bb/0x290
>>>   netlink_sendmsg+0x37c/0x4e0
>>>   sock_sendmsg+0x5f/0x70
>>>   ____sys_sendmsg+0x208/0x280
>>>
>>> In attach_one_default_qdisc(), release the old one before attaching
>>> a new qdisc to fix this bug.
>>>
>>> Fixes: bf6dba76d278 ("net: sched: fallback to qdisc noqueue if 
>>> default qdisc setup fail")
>>> Signed-off-by: Wang Hai <[email-masked]>
>>> ---
>>>   net/sched/sch_generic.c | 5 +++++
>>>   1 file changed, 5 insertions(+)
>>>
>>> diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
>>> index d47b9689eba6..87b61ef14497 100644
>>> --- a/net/sched/sch_generic.c
>>> +++ b/net/sched/sch_generic.c
>>> @@ -1140,6 +1140,11 @@ static void attach_one_default_qdisc(struct 
>>> net_device *dev,
>>>         if (!netif_is_multiqueue(dev))
>>>           qdisc->flags |= TCQ_F_ONETXQUEUE | TCQ_F_NOPARENT;
>>> +
>>> +    if (dev_queue->qdisc_sleeping &&
>>> +        dev_queue->qdisc_sleeping != &noop_qdisc)
>>> +        qdisc_put(dev_queue->qdisc_sleeping);
>>> +
>>>       dev_queue->qdisc_sleeping = qdisc;
>>>   }
>> .
>
-- 
Wang Hai