Re: [PATCH] virtio-rng: complete have_data completion in removing device

On (Wed) 06 Aug 2014 [16:05:41], Amos Kong wrote:

On Wed, Aug 06, 2014 at 01:35:15AM +0800, Amos Kong wrote:

quoted

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