From: Eric Dumazet <eric.dumazet@gmail.com>
To: Yunsheng Lin <linyunsheng@huawei.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
Subject: Re: [PATCH net-next] net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc
Date: Tue, 1 Sep 2020 08:48:12 +0200 [thread overview]
Message-ID: <2d93706f-3ba6-128b-738a-b063216eba6d@gmail.com> (raw)
In-Reply-To: <1598921718-79505-1-git-send-email-linyunsheng@huawei.com>
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.
> 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.
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().
This lockless pfifo_fast is a mess really.
next prev parent reply other threads:[~2020-09-01 6:48 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 [this message]
2020-09-01 7:27 ` Yunsheng Lin
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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