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

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Date:	Sat, 05 Jan 2013 11:37:30 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	davem@...emloft.net, mst@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 3/3] tuntap: don't add to waitqueue when POLLERR

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@...hat.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.



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