From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH net] tuntap: raise EPOLLOUT on device up Date: Tue, 22 May 2018 11:22:11 +0800 Message-ID: <358628f8-a296-ad0e-985b-307895ed5520@redhat.com> References: <1526648443-24128-1-git-send-email-jasowang@redhat.com> <20180521.114742.427929977852677864.davem@davemloft.net> <20180522010700-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, hannes@stressinduktion.org, edumazet@google.com To: "Michael S. Tsirkin" , David Miller Return-path: Received: from mx3-rdu2.redhat.com ([66.187.233.73]:44504 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751505AbeEVDWT (ORCPT ); Mon, 21 May 2018 23:22:19 -0400 In-Reply-To: <20180522010700-mutt-send-email-mst@kernel.org> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 2018年05月22日 06:08, Michael S. Tsirkin wrote: > On Mon, May 21, 2018 at 11:47:42AM -0400, David Miller wrote: >> From: Jason Wang >> Date: Fri, 18 May 2018 21:00:43 +0800 >> >>> We return -EIO on device down but can not raise EPOLLOUT after it was >>> up. This may confuse user like vhost which expects tuntap to raise >>> EPOLLOUT to re-enable its TX routine after tuntap is down. This could >>> be easily reproduced by transmitting packets from VM while down and up >>> the tap device. Fixing this by set SOCKWQ_ASYNC_NOSPACE on -EIO. >>> >>> Cc: Hannes Frederic Sowa >>> Cc: Eric Dumazet >>> Fixes: 1bd4978a88ac2 ("tun: honor IFF_UP in tun_get_user()") >>> Signed-off-by: Jason Wang >> I'm no so sure what to do with this patch. >> >> Like Michael says, this flag bit is only checks upon transmit which >> may or may not happen after this point. It doesn't seem to be >> guaranteed. The flag is checked in tun_chr_poll() as well. > Jason, can't we detect a link up transition and respond accordingly? > What do you think? > I think we've already tried to do this, in tun_net_open() we call write_space(). But the problem is the bit may not be set at that time. A second thought is to set the bit in tun_chr_poll() instead of -EIO like: diff --git a/drivers/net/tun.c b/drivers/net/tun.c index d45ac37..46a1573 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1423,6 +1423,13 @@ static void tun_net_init(struct net_device *dev)         dev->max_mtu = MAX_MTU - dev->hard_header_len;  } +static bool tun_sock_writeable(struct tun_struct *tun, struct tun_file *tfile) +{ +       struct sock *sk = tfile->socket.sk; + +       return (tun->dev->flags & IFF_UP) && sock_writeable(sk); +} +  /* Character device part */  /* Poll */ @@ -1445,10 +1452,9 @@ static __poll_t tun_chr_poll(struct file *file, poll_table *wait)         if (!ptr_ring_empty(&tfile->tx_ring))                 mask |= EPOLLIN | EPOLLRDNORM; -       if (tun->dev->flags & IFF_UP && -           (sock_writeable(sk) || -            (!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags) && -             sock_writeable(sk)))) +       if (tun_sock_writeable(tun, tfile) || +           (!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags) && +            tun_sock_writeable(tun, tfile)));                 mask |= EPOLLOUT | EPOLLWRNORM;         if (tun->dev->reg_state != NETREG_REGISTERED) Does this make more sense? Thanks