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 18:17:32 +0800 Message-ID: <51E9123C.5040708@redhat.com> References: <51E8E4D6.7030807@redhat.com> <20130719072113.GL3087@amit-x200.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130719072113.GL3087@amit-x200.redhat.com> 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 03:48 PM, Amit Shah wrote: > On (Fri) 19 Jul 2013 [15:03:50], Jason Wang wrote: >> 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. > unplug_port() calls wake_up_interruptible on the waitqueue. I mean the following cases: CPU0: CPU1: unplug_port() if (!port->guest_connected) { return POLLHUP; } wake_up_interruptiable() poll_wait(filp, &port->waitqueue, wait); But since it was existed even w/o this series. I agree to keep it as is and fix on top. Other looks good. Thanks > > (But the wake_up should be done after guest_connected is set to > false -- regression introduced in patch 7.) > > Amit