From: Yunsheng Lin <linyunsheng@huawei.com>
To: Eric Dumazet <eric.dumazet@gmail.com>, <jhs@mojatatu.com>,
<xiyou.wangcong@gmail.com>, <jiri@resnulli.us>,
<davem@davemloft.net>, <kuba@kernel.org>
Cc: <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<linuxarm@huawei.com>, <john.fastabend@gmail.com>
Subject: Re: [PATCH net-next] net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc
Date: Tue, 1 Sep 2020 15:27:44 +0800 [thread overview]
Message-ID: <2b60e7fd-a86a-89ab-2759-e7a83e0e28cd@huawei.com> (raw)
In-Reply-To: <2d93706f-3ba6-128b-738a-b063216eba6d@gmail.com>
On 2020/9/1 14:48, Eric Dumazet wrote:
>
>
> On 8/31/20 5:55 PM, Yunsheng Lin wrote:
>> Currently there is concurrent reset and enqueue operation for the
>> same lockless qdisc when there is no lock to synchronize the
>> q->enqueue() in __dev_xmit_skb() with the qdisc reset operation in
>> qdisc_deactivate() called by dev_deactivate_queue(), which may cause
>> out-of-bounds access for priv->ring[] in hns3 driver if user has
>> requested a smaller queue num when __dev_xmit_skb() still enqueue a
>> skb with a larger queue_mapping after the corresponding qdisc is
>> reset, and call hns3_nic_net_xmit() with that skb later.
>>
>> Avoid the above concurrent op by calling synchronize_rcu_tasks()
>> after assigning new qdisc to dev_queue->qdisc and before calling
>> qdisc_deactivate() to make sure skb with larger queue_mapping
>> enqueued to old qdisc will always be reset when qdisc_deactivate()
>> is called.
>>
>
> We request Fixes: tag for fixes in networking land.
ok.
Fixes: 6b3ba9146fe6 ("net: sched: allow qdiscs to handle locking")
>
>> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
>> ---
>> net/sched/sch_generic.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
>> index 265a61d..6e42237 100644
>> --- a/net/sched/sch_generic.c
>> +++ b/net/sched/sch_generic.c
>> @@ -1160,8 +1160,13 @@ static void dev_deactivate_queue(struct net_device *dev,
>>
>> qdisc = rtnl_dereference(dev_queue->qdisc);
>> if (qdisc) {
>> - qdisc_deactivate(qdisc);
>> rcu_assign_pointer(dev_queue->qdisc, qdisc_default);
>> +
>> + /* Make sure lockless qdisc enqueuing is done with the
>> + * old qdisc in __dev_xmit_skb().
>> + */
>> + synchronize_rcu_tasks();
>
> This seems quite wrong, there is not a single use of synchronize_rcu_tasks() in net/,
> we probably do not want this.
>
> I bet that synchronize_net() is appropriate, if not please explain/comment why we want this instead.
Using synchronize_net() seems more appropriate here, thanks.
>
> Adding one synchronize_net() per TX queue is a killer for devices with 128 or 256 TX queues.
>
> I would rather find a way of not calling qdisc_reset() from qdisc_deactivate().
Without calling qdisc_reset(), it seems there will always be skb left in the old qdisc.
Is above acceptable?
How about below steps to avoid the concurrent op:
1. assign new qdisc to all queue' qdisc(which is noop_qdisc).
2. call synchronize_net().
3. calling qdisc_reset() with all queue' qdisc_sleeping.
And the synchronize_net() in dev_deactivate_many() can be reused to
ensure old qdisc is not touched any more when calling qdisc_reset().
>
> This lockless pfifo_fast is a mess really.
>
>
> .
>
next prev parent reply other threads:[~2020-09-01 7:27 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-01 0:55 [PATCH net-next] net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc Yunsheng Lin
2020-09-01 6:48 ` Eric Dumazet
2020-09-01 7:27 ` Yunsheng Lin [this message]
2020-09-01 18:34 ` David Miller
2020-09-02 1:43 ` Yunsheng Lin
2020-09-01 18:24 ` Cong Wang
2020-09-02 1:42 ` Yunsheng Lin
2020-09-02 4:41 ` Cong Wang
2020-09-02 6:34 ` Yunsheng Lin
2020-09-02 7:32 ` Eric Dumazet
2020-09-02 8:14 ` Yunsheng Lin
2020-09-02 9:20 ` Eric Dumazet
2020-09-03 1:14 ` Yunsheng Lin
2020-09-03 7:24 ` Eric Dumazet
2020-09-04 8:10 ` Yunsheng Lin
2020-09-03 0:35 ` Cong Wang
2020-09-03 1:21 ` Yunsheng Lin
2020-09-03 1:48 ` Cong Wang
2020-09-03 2:22 ` Yunsheng Lin
2020-09-03 2:53 ` Cong Wang
2020-09-04 1:30 ` John Fastabend
2020-09-04 8:08 ` Yunsheng Lin
2020-09-06 8:52 ` [net] 6fd0d0dede: hwsim.ap_ht40_5ghz_switch.fail kernel test robot
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