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Date:   Tue, 3 Mar 2020 16:46:56 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Tommi Rantala <tommi.t.rantala@nokia.com>
Cc:     stable@vger.kernel.org, Jason Wang <jasowang@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4.14] tuntap: correctly set SOCKWQ_ASYNC_NOSPACE
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On Fri, Feb 28, 2020 at 10:42:16AM +0200, Tommi Rantala wrote:
> From: Jason Wang <jasowang@redhat.com>
> 
> [ Upstream commit 2f3ab6221e4c87960347d65c7cab9bd917d1f637 ]
> 
> 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: Tommi Rantala <tommi.t.rantala@nokia.com>
> ---
>  drivers/net/tun.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)

Thanks for the backport, now queued up to 4.9.y and 4.14.y.

greg k-h