From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752661AbeEROAl (ORCPT ); Fri, 18 May 2018 10:00:41 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:35438 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752177AbeEROAi (ORCPT ); Fri, 18 May 2018 10:00:38 -0400 Subject: Re: [PATCH net] tuntap: raise EPOLLOUT on device up From: Jason Wang To: "Michael S. Tsirkin" Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Hannes Frederic Sowa , Eric Dumazet References: <1526648443-24128-1-git-send-email-jasowang@redhat.com> <20180518161253-mutt-send-email-mst@kernel.org> Message-ID: <6159b23e-eeda-1d4b-6a30-63b1a30666eb@redhat.com> Date: Fri, 18 May 2018 22:00:31 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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