Re: [PATCH 2/3] hw/virtio: Remove NULL check in virtio_free_region_cache()

[Stefan Hajnoczi]

On Thu, Aug 26, 2021 at 07:26:57PM +0200, Philippe Mathieu-Daudé wrote:
> virtio_free_region_cache() is called within call_rcu(),
> always with a non-NULL argument. Ensure new code keep it
> that way by replacing the NULL check by an assertion.
> Add a comment this function is called within call_rcu().
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  hw/virtio/virtio.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index a5214bca612..3a1f6c520cb 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -133,12 +133,10 @@ struct VirtQueue
>      QLIST_ENTRY(VirtQueue) node;
>  };
>  
> +/* Called within call_rcu().  */
>  static void virtio_free_region_cache(VRingMemoryRegionCaches *caches)
>  {
> -    if (!caches) {
> -        return;
> -    }
> -
> +    assert(caches != NULL);
>      address_space_cache_destroy(&caches->desc);
>      address_space_cache_destroy(&caches->avail);
>      address_space_cache_destroy(&caches->used);

Looks like an artifact that was left in when the code was originally
introduced in commit c611c76417f52b335ecaab01c61743e3b705eb7c ("virtio:
add MemoryListener to cache ring translations"). Paolo could confirm
this.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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