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 12:00:54 +0800 Message-ID: <8fa1a828-c1a7-65c0-5f15-ebb215402dcb@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> <358628f8-a296-ad0e-985b-307895ed5520@redhat.com> <20180522064529-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: David Miller , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, hannes@stressinduktion.org, edumazet@google.com To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20180522064529-mutt-send-email-mst@kernel.org> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 2018年05月22日 11:46, Michael S. Tsirkin wrote: > On Tue, May 22, 2018 at 11:22:11AM +0800, Jason Wang wrote: >> >> 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 > I just understood the motivation for doing it on EIO. > Maybe there's a reason it makes sense here as well, > but it's far from obvious. I suggest you repost adding > an explanation in the comment. The original patch will > be fine with an explanation as well. > Ok, let me add explanation on both code and commit log. Thanks