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





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