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Message-ID: <fc76cc5d-e1ee-e84e-c47b-8daa4dea43a0@huawei.com>
Date: Thu, 25 Aug 2022 20:29:21 +0800
From: "wanghai (M)" <wanghai38@...wei.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: <jhs@...atatu.com>, <xiyou.wangcong@...il.com>, <jiri@...nulli.us>,
<davem@...emloft.net>, <edumazet@...gle.com>, <pabeni@...hat.com>,
<brouer@...hat.com>, <netdev@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net/sched: fix netdevice reference leaks in
attach_one_default_qdisc()
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 <wanghai38@...wei.com>
>>> ---
>>> 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
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