Re: [PATCH v3 2/3] hw/virtio: Acquire RCU read lock in virtqueue_packed_drop_all()

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Mon, Sep 06, 2021 at 12:43:17PM +0200, Philippe Mathieu-Daudé wrote:
> vring_get_region_caches() must be called with the RCU read lock
> acquired. virtqueue_packed_drop_all() does not, and uses the
> 'caches' pointer. Fix that by using the RCU_READ_LOCK_GUARD()
> macro.

Is this a bug that has been encountered, is it a latent bug, a code
cleanup, etc? The impact of this isn't clear but it sounds a little
scary so I wanted to check.

> 
> Reported-by: Stefano Garzarella <sgarzare@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  hw/virtio/virtio.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 97f60017466..7d3bf9091ee 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -1704,6 +1704,8 @@ static unsigned int virtqueue_packed_drop_all(VirtQueue *vq)
>      VirtIODevice *vdev = vq->vdev;
>      VRingPackedDesc desc;
>  
> +    RCU_READ_LOCK_GUARD();
> +
>      caches = vring_get_region_caches(vq);
>      if (!caches) {
>          return 0;
> -- 
> 2.31.1
> 

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