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Mon, 31 Aug 2020 23:48:14 -0700 (PDT) Subject: Re: [PATCH net-next] net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc To: Yunsheng Lin , 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 References: <1598921718-79505-1-git-send-email-linyunsheng@huawei.com> From: Eric Dumazet Message-ID: <2d93706f-3ba6-128b-738a-b063216eba6d@gmail.com> Date: Tue, 1 Sep 2020 08:48:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <1598921718-79505-1-git-send-email-linyunsheng@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > --- > 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.