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 <han...@stressinduktion.org>
> Cc: Eric Dumazet <eduma...@google.com>
> Fixes: 1bd4978a88ac2 ("tun: honor IFF_UP in tun_get_user()")
> Signed-off-by: Jason Wang <jasow...@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?
> + set_bit(SOCKWQ_ASYNC_NOSPACE, &tfile->socket.flags);
> return -EIO;
> + }
>
> if (!(tun->flags & IFF_NO_PI)) {
> if (len < sizeof(pi))
> --
> 2.7.4
