From: Jason Wang <jasowang@redhat.com>
To: Eric Dumazet <eric.dumazet@gmail.com>, netdev@vger.kernel.org
Cc: mst@redhat.com, YueHaibing <yuehaibing@huawei.com>,
Cong Wang <xiyou.wangcong@gmail.com>,
"weiyongjun (A)" <weiyongjun1@huawei.com>
Subject: Re: [PATCH net] tuntap: synchronize through tfiles array instead of tun->numqueues
Date: Tue, 7 May 2019 11:54:00 +0800 [thread overview]
Message-ID: <6f880c3e-ebb6-a683-6c75-c94409a60741@redhat.com> (raw)
In-Reply-To: <7b9744b4-42ec-7d0a-20ff-d65f71b16c63@gmail.com>
On 2019/5/7 上午11:41, Eric Dumazet wrote:
>
> On 5/6/19 11:23 PM, Jason Wang wrote:
>> When a queue(tfile) is detached through __tun_detach(), we move the
>> last enabled tfile to the position where detached one sit but don't
>> NULL out last position. We expect to synchronize the datapath through
>> tun->numqueues. Unfortunately, this won't work since we're lacking
>> sufficient mechanism to order or synchronize the access to
>> tun->numqueues.
>>
>> To fix this, NULL out the last position during detaching and check
>> RCU protected tfile against NULL instead of checking tun->numqueues in
>> datapath.
>>
>> Cc: YueHaibing <yuehaibing@huawei.com>
>> Cc: Cong Wang <xiyou.wangcong@gmail.com>
>> Cc: weiyongjun (A) <weiyongjun1@huawei.com>
>> Fixes: c8d68e6be1c3b ("tuntap: multiqueue support")
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>> drivers/net/tun.c | 12 +++++++-----
>> 1 file changed, 7 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>> index e9ca1c0..a64c928 100644
>> --- a/drivers/net/tun.c
>> +++ b/drivers/net/tun.c
>> @@ -700,6 +700,8 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
>> tun->tfiles[tun->numqueues - 1]);
>> ntfile = rtnl_dereference(tun->tfiles[index]);
>> ntfile->queue_index = index;
>> + rcu_assign_pointer(tun->tfiles[tun->numqueues - 1],
>> + NULL);
>>
>> --tun->numqueues;
>> if (clean) {
>> @@ -1082,7 +1084,7 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>> tfile = rcu_dereference(tun->tfiles[txq]);
>>
>> /* Drop packet if interface is not attached */
>> - if (txq >= tun->numqueues)
>> + if (!tfile)
>> goto drop;
>>
>> if (!rcu_dereference(tun->steering_prog))
>> @@ -1306,13 +1308,13 @@ static int tun_xdp_xmit(struct net_device *dev, int n,
>> rcu_read_lock();
>>
>> numqueues = READ_ONCE(tun->numqueues);
>> - if (!numqueues) {
>> - rcu_read_unlock();
>> - return -ENXIO; /* Caller will free/return all frames */
>> - }
>>
> If you remove the test on (!numqueues),
> the following might crash with a divide by zero...
Indeed, let me post V2.
Thanks
>
>> tfile = rcu_dereference(tun->tfiles[smp_processor_id() %
>> numqueues]);
next prev parent reply other threads:[~2019-05-07 3:54 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-07 3:23 [PATCH net] tuntap: synchronize through tfiles array instead of tun->numqueues Jason Wang
2019-05-07 3:41 ` Eric Dumazet
2019-05-07 3:54 ` Jason Wang [this message]
2019-05-07 14:47 ` Eric Dumazet
2019-05-08 2:54 ` Jason Wang
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