Re: [PATCH V2 3/3] tuntap: don't add to waitqueue when POLLERR

[Eric Dumazet <eric.dumazet@gmail.com>]

On Sat, 2013-01-05 at 17:34 +0800, Jason Wang wrote:
> Currently, tun_chr_poll() returns POLLERR after waitqueue adding during device
> unregistration. This would confuse some of its user such as vhost which assume
> when POLLERR is returned, it wasn't added to the waitqueue. Fix this by
> returning POLLERR before adding to waitqueue.
> 
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  drivers/net/tun.c |    5 +----
>  1 files changed, 1 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index fbd106e..f9c0049 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -886,7 +886,7 @@ static unsigned int tun_chr_poll(struct file *file, poll_table *wait)
>  	struct sock *sk;
>  	unsigned int mask = 0;
>  
> -	if (!tun)
> +	if (!tun || tun->dev->reg_state != NETREG_REGISTERED)
>  		return POLLERR;
>  
>  	sk = tfile->socket.sk;
> @@ -903,9 +903,6 @@ static unsigned int tun_chr_poll(struct file *file, poll_table *wait)
>  	     sock_writeable(sk)))
>  		mask |= POLLOUT | POLLWRNORM;
>  
> -	if (tun->dev->reg_state != NETREG_REGISTERED)
> -		mask = POLLERR;
> -
>  	tun_put(tun);
>  	return mask;
>  }

This patch is buggy.

First, the caller assuming POLLERR means poll_wait() was not called is
wrong.

Secondly, you add a ref leak.