[PATCH v2 1/2] virtio: Reduce BUG if total_sg > virtqueue size to WARN.

[Richard W.M. Jones]

If using indirect descriptors, you can make the total_sg as large as
you want.  If not, BUG is too serious because the function later
returns -ENOSPC.

Thanks Paolo Bonzini, Christoph Hellwig.

Signed-off-by: Richard W.M. Jones <rjo...@redhat.com>
Reviewed-by: Paolo Bonzini <pbonz...@redhat.com>
---
 drivers/virtio/virtio_ring.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 5e1b548828e6..27cbc1eab868 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -296,7 +296,6 @@ static inline int virtqueue_add(struct virtqueue *_vq,
        }
 #endif
 
-       BUG_ON(total_sg > vq->vring.num);
        BUG_ON(total_sg == 0);
 
        head = vq->free_head;
@@ -305,8 +304,10 @@ static inline int virtqueue_add(struct virtqueue *_vq,
         * buffers, then go indirect. FIXME: tune this threshold */
        if (vq->indirect && total_sg > 1 && vq->vq.num_free)
                desc = alloc_indirect(_vq, total_sg, gfp);
-       else
+       else {
                desc = NULL;
+               WARN_ON_ONCE(total_sg > vq->vring.num && !vq->indirect);
+       }
 
        if (desc) {
                /* Use a single buffer which doesn't continue */
-- 
2.13.1