linux-kernel - [PATCH v2 1/2] virtio: Reduce BUG if total

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Date:   Thu, 10 Aug 2017 17:56:51 +0100
From:   "Richard W.M. Jones" <rjones@...hat.com>
To:     jejb@...ux.vnet.ibm.com
Cc:     martin.petersen@...cle.com, mst@...hat.com, jasowang@...hat.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, hch@....de,
        pbonzini@...hat.com
Subject: [PATCH v2 1/2] virtio: Reduce BUG if total_sg > virtqueue size to WARN.

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 <rjones@...hat.com>
Reviewed-by: Paolo Bonzini <pbonzini@...hat.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