Re: [stable] [PATCH] virtio: fix oops on OOM

[Chuck Ebbert <cebbert@redhat.com>]

On Fri, 23 Jul 2010 15:48:37 +0930
Rusty Russell <rusty@rustcorp.com.au> wrote:

Note that commit 686d363786a53ed28ee875b84ef24e6d5126ef6f,
which caused this problem, is already queued for -stable,
so it should either be removed or this should be sent for
-stable as well.

> From: "Michael S. Tsirkin" <mst@redhat.com>
> 
> 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@oracle.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
> Tested-by: Chris Mason <chris.mason@oracle.com>
> ---
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index dd35b34..bffec32 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -164,7 +164,8 @@ int virtqueue_add_buf_gfp(struct virtqueue *_vq,
>  			  gfp_t gfp)
>  {
>  	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);
>  
> @@ -174,8 +175,8 @@ int virtqueue_add_buf_gfp(struct virtqueue *_vq,
>  	 * 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, gfp);
> -		if (head != vq->vring.num)
> +		if (likely(head >= 0))
>  			goto add_head;
>  	}
>  
>  	BUG_ON(out + in > vq->vring.num);
> --