Messages in this thread | | | Subject | Re: [PATCH net] tuntap: raise EPOLLOUT on device up | From | Jason Wang <> | Date | Fri, 18 May 2018 22:11:54 +0800 |
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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
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