linux-kernel - [106/205] virtio: fix oops on OOM

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Message-Id: <20100730175143.447230105@clark.site>
Date:	Fri, 30 Jul 2010 10:52:03 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: [106/205] virtio: fix oops on OOM

2.6.34-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Michael S. Tsirkin <mst@...hat.com>

commit 1fe9b6fef11771461e69ecd1bc8935a1c7c90cb5 upstream.

virtio ring was changed to return an error code on OOM,
but one caller was missed and still checks for vq->vring.num.
The fix is just to check for <0 error code.

Long term it might make sense to change goto add_head to
just return an error on oom instead, but let's apply
a minimal fix for 2.6.35.

Reported-by: Chris Mason <chris.mason@...cle.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
Tested-by: Chris Mason <chris.mason@...cle.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/virtio/virtio_ring.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -162,7 +162,8 @@ static int vring_add_buf(struct virtqueu
 			 void *data)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
-	unsigned int i, avail, head, uninitialized_var(prev);
+	unsigned int i, avail, uninitialized_var(prev);
+	int head;

 	START_USE(vq);

@@ -172,7 +173,7 @@ static int vring_add_buf(struct virtqueu
 	 * buffers, then go indirect. FIXME: tune this threshold */
 	if (vq->indirect && (out + in) > 1 && vq->num_free) {
 		head = vring_add_indirect(vq, sg, out, in);
-		if (head != vq->vring.num)
+		if (likely(head >= 0))
 			goto add_head;
 	}

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