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tuntap: correctly set SOCKWQ_ASYNC_NOSPACE

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When link is down, writes to the device might fail with
-EIO. Userspace needs an indication when the status is resolved.  As a
fix, tun_net_open() attempts to wake up writers - but that is only
effective if SOCKWQ_ASYNC_NOSPACE has been set in the past. This is
not the case of vhost_net which only poll for EPOLLOUT after it meets
errors during sendmsg().

This patch fixes this by making sure SOCKWQ_ASYNC_NOSPACE is set when
socket is not writable or device is down to guarantee EPOLLOUT will be
raised in either tun_chr_poll() or tun_sock_write_space() after device
is up.

Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Eric Dumazet <edumazet@google.com>
Fixes: 1bd4978a88 ("tun: honor IFF_UP in tun_get_user()")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jason Wang 2018-05-22 14:21:04 +08:00 committed by David S. Miller
parent a43ad59a90
commit 2f3ab6221e
1 changed files with 15 additions and 4 deletions
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19
drivers/net/tun.c
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@ -1423,6 +1423,13 @@ static void tun_net_init(struct net_device *dev)
dev->max_mtu = MAX_MTU - dev->hard_header_len;
}
static bool tun_sock_writeable(struct tun_struct *tun, struct tun_file *tfile)
{
struct sock *sk = tfile->socket.sk;
return (tun->dev->flags & IFF_UP) && sock_writeable(sk);
}
/* Character device part */
/* Poll */
@ -1445,10 +1452,14 @@ static __poll_t tun_chr_poll(struct file *file, poll_table *wait)
if (!ptr_ring_empty(&tfile->tx_ring))
mask |= EPOLLIN | EPOLLRDNORM;
if (tun->dev->flags & IFF_UP &&
(sock_writeable(sk) ||
(!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags) &&
sock_writeable(sk))))
/* Make sure SOCKWQ_ASYNC_NOSPACE is set if not writable to
* guarantee EPOLLOUT to be raised by either here or
* tun_sock_write_space(). Then process could get notification
* after it writes to a down device and meets -EIO.
*/
if (tun_sock_writeable(tun, tfile) ||
(!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags) &&
tun_sock_writeable(tun, tfile)))
mask |= EPOLLOUT | EPOLLWRNORM;
if (tun->dev->reg_state != NETREG_REGISTERED)