On (Wed) 06 Aug 2014 [16:05:41], Amos Kong wrote:
> On Wed, Aug 06, 2014 at 01:35:15AM +0800, Amos Kong wrote:
> > When we try to hot-remove a busy virtio-rng device from QEMU monitor,
> > the device can't be hot-removed. Because virtio-rng driver hangs at
> > wait_for_completion_killable().
> >
> > This patch fixed the hang by completing have_data completion before
> > unregistering a virtio-rng device.
>
> Hi Amit,
>
> Before applying this patch, it's blocking insider
> wait_for_completion_killable()
> Applied this patch, wait_for_completion_killable() returns 0,
> and vi->data_avail becomes 0, then rng_get_date() will return 0.
Thanks for checking this.
> Is it expected result?
I think what will happen is vi->data_avail will be set to whatever it
was set last. In case of a previous successful read request, the
data_avail will be set to whatever number of bytes the host gave. On
doing a hot-unplug on the succeeding wait, the value in data_avail
will be re-used, and the hwrng core will wrongly take some bytes in
the buffer as input from the host.
So, I think we need to set vi->data_avail = 0; before calling
wait_event_completion_killable().
Amit
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