[Devel] [PATCH vz7.39] scsi: virtio: Reduce BUG if total_sg > virtqueue size to WARN.

[Denis V. Lunev]

On 12/19/2017 04:02 PM, Roman Kagan wrote:
> From: "Richard W.M. Jones" <rjones at redhat.com>
>
> 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.
>
> Signed-off-by: Richard W.M. Jones <rjones at redhat.com>
> Reviewed-by: Paolo Bonzini <pbonzini at redhat.com>
> Signed-off-by: Martin K. Petersen <martin.petersen at oracle.com>
> (cherry picked from commit 44ed8089e991a60d614abe0ee4b9057a28b364e4)
> Signed-off-by: Roman Kagan <rkagan at virtuozzo.com>
> VZ-Bug: PSBM-79523
> ---
>  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 d77a91f39d55..5903139aede2 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -275,7 +275,6 @@ 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;
> @@ -284,8 +283,10 @@ 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 */
Kostya, can you pls schedule a build?
QA wanted this very much.

Den