[PATCH 4.9 45/88] tuntap: correctly set SOCKWQ_ASYNC_NOSPACE

Greg Kroah-Hartman
2020-03-10T13:34:59Z

From: Jason Wang <jasowang@redhat.com>

commit 2f3ab6221e4c87960347d65c7cab9bd917d1f637 upstream.

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: 1bd4978a88ac2 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tommi Rantala <tommi.t.rantala@nokia.com>

---
drivers/net/tun.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1106,6 +1106,13 @@ static void tun_net_init(struct net_devi
}
}

+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 */
@@ -1128,10 +1135,14 @@ static unsigned int tun_chr_poll(struct
if (!skb_array_empty(&tfile->tx_array))
mask |= POLLIN | POLLRDNORM;

- 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 |= POLLOUT | POLLWRNORM;

if (tun->dev->reg_state != NETREG_REGISTERED)