Messages in this thread | | | Subject | Re: [PATCH net] tuntap: raise EPOLLOUT on device up | From | Jason Wang <> | Date | Sat, 19 May 2018 09:09:11 +0800 |
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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 <hannes@stressinduktion.org> >>>>>>> Cc: Eric Dumazet <edumazet@google.com> >>>>>>> Fixes: 1bd4978a88ac2 ("tun: honor IFF_UP in tun_get_user()") >>>>>>> Signed-off-by: Jason Wang <jasowang@redhat.com> >>>>>>> --- >>>>>>> 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 <jasowang@redhat.com> >> 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
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