Re: [PATCH] vhost: fix read vs write lock mismatch

[David Marchand <david.marchand@redhat.com>]

On Mon, Nov 18, 2024 at 5:24 PM Stephen Hemminger
<stephen@networkplumber.org> wrote:
>
> If lock is acquired for write, it must be released for write
> or a deadlock is likely.
>
> Bugzilla ID: 1582
> Fixes: 9fc93a1e2320 ("vhost: fix virtqueue access check in datapath")
> Cc: david.marchand@redhat.com
> Cc: stable@dpdk.org
>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>  lib/vhost/virtio_net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> index 298a5dae74..d764d4bc6a 100644
> --- a/lib/vhost/virtio_net.c
> +++ b/lib/vhost/virtio_net.c
> @@ -2538,7 +2538,7 @@ virtio_dev_rx_async_submit(struct virtio_net *dev, struct vhost_virtqueue *vq,
>
>         if (unlikely(!vq->access_ok)) {
>                 vhost_user_iotlb_rd_unlock(vq);
> -               rte_rwlock_read_unlock(&vq->access_lock);
> +               rte_rwlock_write_unlock(&vq->access_lock);

A write lock is taken earlier, because virtio_dev_rx_async_submit_*
need it for access to vq->async (as opposed to the sync code that only
takes read lock).

Here, no need to release/take again all locks.
A simpler fix is to directly call vring_translate(dev, vq).


-- 
David Marchand