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: Fri, 18 May 2018 16:13:36 +0300 Message-ID: <20180518161253-mutt-send-email-mst@kernel.org> References: <1526648443-24128-1-git-send-email-jasowang@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii 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: <1526648443-24128-1-git-send-email-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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? > + set_bit(SOCKWQ_ASYNC_NOSPACE, &tfile->socket.flags); > return -EIO; > + } > > if (!(tun->flags & IFF_NO_PI)) { > if (len < sizeof(pi)) > -- > 2.7.4