Re: [PATCH net] tuntap: raise EPOLLOUT on device up
From: Jason Wang
Date: Fri May 18 2018 - 09:15:57 EST
On 2018å05æ18æ 22:06, Michael S. Tsirkin wrote:
On Fri, May 18, 2018 at 10:00:31PM +0800, Jason Wang wrote:
On 2018å05æ18æ 21:26, Jason Wang wrote:
On 2018å05æ18æ 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@xxxxxxxxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Fixes: 1bd4978a88ac2 ("tun: honor IFF_UP in tun_get_user()")
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 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,
ÂÂÂÂÂ int skb_xdp = 1;
ÂÂÂÂÂ bool frags = tun_napi_frags_enabled(tun);
 - if (!(tun->dev->flags & IFF_UP))
+ÂÂÂ 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@xxxxxxxxxx>
Date:ÂÂ Mon Nov 13 11:45:34 2017 +0800
ÂÂÂ vhost_net: conditionally enable tx polling
Thanks