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

From	"Richard W.M. Jones" <rjones@redhat.com>
Newsgroups	linux.kernel
Subject	[PATCH v2 1/2] virtio: Reduce BUG if total_sg > virtqueue size to WARN.
Date	2017-08-10 19:00 +0200
Message-ID	<ucYYr-8ev-39@gated-at.bofh.it> (permalink)
References	<ucYYr-8ev-35@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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

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[PATCH v2 1/2] virtio: Reduce BUG if total_sg > virtqueue size to WARN. "Richard W.M. Jones" <rjones@redhat.com> - 2017-08-10 19:00 +0200

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