Linux Virtualization - Aug 2014 - [PATCH] virtio-rng: complete have_data completion in removing device

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.

Signed-off-by: Amos Kong <akong at redhat.com>
Cc: stable at vger.kernel.org
---
 drivers/char/hw_random/virtio-rng.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/char/hw_random/virtio-rng.c
b/drivers/char/hw_random/virtio-rng.c
index 0027137..416b15c 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -137,6 +137,7 @@ static void remove_common(struct virtio_device *vdev)
 	struct virtrng_info *vi = vdev->priv;
 
 	vdev->config->reset(vdev);
+	complete(&vi->have_data);
 	vi->busy = false;
 	if (vi->hwrng_register_done)
 		hwrng_unregister(&vi->hwrng);
-- 
1.9.3

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.

Is it expected result?

 
> Signed-off-by: Amos Kong <akong at redhat.com>
> Cc: stable at vger.kernel.org
> ---
>  drivers/char/hw_random/virtio-rng.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/char/hw_random/virtio-rng.c
b/drivers/char/hw_random/virtio-rng.c
> index 0027137..416b15c 100644
> --- a/drivers/char/hw_random/virtio-rng.c
> +++ b/drivers/char/hw_random/virtio-rng.c
> @@ -137,6 +137,7 @@ static void remove_common(struct virtio_device *vdev)
>  	struct virtrng_info *vi = vdev->priv;
>  
>  	vdev->config->reset(vdev);
> +	complete(&vi->have_data);
>  	vi->busy = false;
>  	if (vi->hwrng_register_done)
>  		hwrng_unregister(&vi->hwrng);
> -- 
> 1.9.3
> 
> _______________________________________________
> Virtualization mailing list
> Virtualization at lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/virtualization
-- 
			Amos.

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