virtio: zero vq->inuse in virtio_reset()

vq->inuse must be zeroed upon device reset like most other virtqueue
fields.

In theory, virtio_reset() just needs assert(vq->inuse == 0) since
devices must clean up in-flight requests during reset (requests cannot
not be leaked!).

In practice, it is difficult to achieve vq->inuse == 0 across reset
because balloon, blk, 9p, etc implement various different strategies for
cleaning up requests.  Most devices call g_free(elem) directly without
telling virtio.c that the VirtQueueElement is cleaned up.  Therefore
vq->inuse is not decremented during reset.

This patch zeroes vq->inuse and trusts that devices are not leaking
VirtQueueElements across reset.

I will send a follow-up series that refactors request life-cycle across
all devices and converts vq->inuse = 0 into assert(vq->inuse == 0) but
this more invasive approach is not appropriate for stable trees.

Signed-off-by: Stefan Hajnoczi <[email protected]>
Cc: qemu-stable <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>
Reviewed-by: Ladi Prosek <[email protected]>

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 74c085c74d266ef7027296ffedd9d230c78e3bd6..e8a13a50bfd7def31a12b59759495ab782062e1e 100644 (file)
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -822,6 +822,7 @@ void virtio_reset(void *opaque)
         vdev->vq[i].signalled_used_valid = false;
         vdev->vq[i].notification = true;
         vdev->vq[i].vring.num = vdev->vq[i].vring.num_default;
+        vdev->vq[i].inuse = 0;
     }
 }