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 <[email protected]>
>>> ---
>>> 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
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