From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH net] tuntap: raise EPOLLOUT on device up Date: Tue, 22 May 2018 01:06:56 +0300 Message-ID: <20180522010618-mutt-send-email-mst@kernel.org> References: <1526648443-24128-1-git-send-email-jasowang@redhat.com> <20180518161253-mutt-send-email-mst@kernel.org> <6159b23e-eeda-1d4b-6a30-63b1a30666eb@redhat.com> <20180518170155-mutt-send-email-mst@kernel.org> <20180518172932-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Hannes Frederic Sowa , Eric Dumazet To: Jason Wang Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Sat, May 19, 2018 at 09:09:11AM +0800, Jason Wang wrote: > > > On 2018年05月18日 22:46, Michael S. Tsirkin wrote: > > On Fri, May 18, 2018 at 10:11:54PM +0800, Jason Wang wrote: > > > > > > On 2018年05月18日 22:06, Michael S. Tsirkin wrote: > > > > On Fri, May 18, 2018 at 10:00:31PM +0800, Jason Wang wrote: > > > > > On 2018年05月18日 21:26, Jason Wang wrote: > > > > > > On 2018年05月18日 21:13, Michael S. Tsirkin wrote: > > > > > > > On Fri, May 18, 2018 at 09:00:43PM +0800, Jason Wang wrote: > > > > > > > > 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 > > > > > > > > --- > > > > > > > >   drivers/net/tun.c | 4 +++- > > > > > > > >   1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > > > > > > > > index d45ac37..1b29761 100644 > > > > > > > > --- a/drivers/net/tun.c > > > > > > > > +++ b/drivers/net/tun.c > > > > > > > > @@ -1734,8 +1734,10 @@ static ssize_t tun_get_user(struct > > > > > > > > tun_struct *tun, struct tun_file *tfile, > > > > > > > >       int skb_xdp = 1; > > > > > > > >       bool frags = tun_napi_frags_enabled(tun); > > > > > > > >   -    if (!(tun->dev->flags & IFF_UP)) > > > > > > > > +    if (!(tun->dev->flags & IFF_UP)) { > > > > > > > Isn't this racy?  What if flag is cleared at this point? > > > > > > I think you mean "set at this point"? Then yes, so we probably need to > > > > > > set the bit during tun_net_close(). > > > > > > > > > > > > Thanks > > > > > Looks no need, vhost will poll socket after it see EIO. So we are ok here? > > > > > > > > > > Thanks > > > > In fact I don't even understand why does this help any longer. > > > > > > > We disable tx polling and only enable it on demand for a better rx > > > performance. You may want to have a look at : > > > > > > commit feb8892cb441c742d4220cf7ced001e7fa070731 > > > Author: Jason Wang > > > Date:   Mon Nov 13 11:45:34 2017 +0800 > > > > > >     vhost_net: conditionally enable tx polling > > > > > > Thanks > > > > Question is, what looks at SOCKWQ_ASYNC_NOSPACE. > > I think it's tested when packet is transmitted, > > but there is no guarantee here any packet will > > ever be transmitted. > > > > Well, actually, I do plan to disable vq polling from the beginning. But > looks like you do not want this: > > See https://patchwork.kernel.org/patch/10034025/ > > Thanks Not sure I understand what you are saying, it's enabling polling we are talking about. -- MST