From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH 06/10] virtio: console: fix race in port_fops_poll() and port unplug Date: Fri, 19 Jul 2013 15:03:50 +0800 Message-ID: <51E8E4D6.7030807@redhat.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Amit Shah Cc: Virtualization List List-Id: virtualization@lists.linuxfoundation.org On 07/19/2013 04:16 AM, Amit Shah wrote: > Between poll() being called and processed, the port can be unplugged. > Check if this happened, and bail out. > > Signed-off-by: Amit Shah > --- > drivers/char/virtio_console.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c > index 7728af9..1d4b748 100644 > --- a/drivers/char/virtio_console.c > +++ b/drivers/char/virtio_console.c > @@ -967,6 +967,10 @@ static unsigned int port_fops_poll(struct file *filp, poll_table *wait) > unsigned int ret; > > port = filp->private_data; > + if (!port->guest_connected) { > + /* Port was unplugged before we could proceed */ > + return POLLHUP; > + } > poll_wait(filp, &port->waitqueue, wait); > > if (!port->guest_connected) { Looks still racy here. Unlike port_fops_read() which check will_read_block(). If unplug happens after the check but before the poll_wait(), caller will be blocked forever.