Virtualization - Sep 2014 - [PATCH v3 1/2] virtio-rng: fix stuck of hot-unplugging busy device

RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1121540

When we try to hot-unplugging a busy virtio-rng device, the device
can't be removed. And the reading process in guest gets stuck.

Those two patches fixed this issue by completing have_data completion
and preventing invalid reading.

Thanks for the help of Amit.

Cc: stable at vger.kernel.org

V2: reset data_avail (Amit)
    adjust unregister order
V3: split patch, update commitlog

Amos Kong (2):
  virtio-rng: fix stuck of hot-unplugging busy device
  virtio-rng: skip reading when we start to remove the device

 drivers/char/hw_random/virtio-rng.c | 7 +++++++
 1 file changed, 7 insertions(+)

-- 
1.9.3

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 exits the waiting by completing have_data completion before
unregistering, resets data_avail to avoid the hwrng core use wrong
buffer bytes.

Signed-off-by: Amos Kong <akong at redhat.com>
Cc: stable at vger.kernel.org
---
 drivers/char/hw_random/virtio-rng.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/char/hw_random/virtio-rng.c
b/drivers/char/hw_random/virtio-rng.c
index 2e3139e..849b228 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -137,6 +137,8 @@ static void remove_common(struct virtio_device *vdev)
 {
 	struct virtrng_info *vi = vdev->priv;
 
+	vi->data_avail = 0;
+	complete(&vi->have_data);
 	vdev->config->reset(vdev);
 	vi->busy = false;
 	if (vi->hwrng_register_done)
-- 
1.9.3

Before we really unregister the hwrng device, reading will get stuck if
the virtio device is reset. We should return error for reading when we
start to remove the device.

Signed-off-by: Amos Kong <akong at redhat.com>
Cc: stable at vger.kernel.org
---
 drivers/char/hw_random/virtio-rng.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/char/hw_random/virtio-rng.c
b/drivers/char/hw_random/virtio-rng.c
index 849b228..132c9cc 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -36,6 +36,7 @@ struct virtrng_info {
 	int index;
 	bool busy;
 	bool hwrng_register_done;
+	bool hwrng_removed;
 };
 
 
@@ -68,6 +69,9 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t
size, bool wait)
 	int ret;
 	struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
 
+	if (vi->hwrng_removed)
+		return -ENODEV;
+
 	if (!vi->busy) {
 		vi->busy = true;
 		init_completion(&vi->have_data);
@@ -137,6 +141,7 @@ static void remove_common(struct virtio_device *vdev)
 {
 	struct virtrng_info *vi = vdev->priv;
 
+	vi->hwrng_removed = true;
 	vi->data_avail = 0;
 	complete(&vi->have_data);
 	vdev->config->reset(vdev);
-- 
1.9.3

On (Wed) 10 Sep 2014 [14:11:36], 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 exits the waiting by completing have_data completion before
> unregistering, resets data_avail to avoid the hwrng core use wrong
> buffer bytes.
> 
> Signed-off-by: Amos Kong <akong at redhat.com>
> Cc: stable at vger.kernel.org
Reviewed-by: Amit Shah <amit.shah at redhat.com>

		Amit

On (Wed) 10 Sep 2014 [14:11:37], Amos Kong wrote:
> Before we really unregister the hwrng device, reading will get stuck if
> the virtio device is reset. We should return error for reading when we
> start to remove the device.
> 
> Signed-off-by: Amos Kong <akong at redhat.com>
> Cc: stable at vger.kernel.org
Reviewed-by: Amit Shah <amit.shah at redhat.com>

		Amit