Re: [PATCH 5/5] virtio_blk: simplify refcounting

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Feb 09, 2022 at 09:21:20AM +0100, Christoph Hellwig wrote:
> Implement the ->free_disk method to free the virtio_blk structure only
> once the last gendisk reference goes away instead of keeping a local
> refcount.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  drivers/block/virtio_blk.c | 74 +++++++++++---------------------------
>  1 file changed, 21 insertions(+), 53 deletions(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index c443cd64fc9b4..05cc5451d6cc1 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -69,13 +69,6 @@ struct virtio_blk {
>  	/* Process context for config space updates */
>  	struct work_struct config_work;
>  
> -	/*
> -	 * Tracks references from block_device_operations open/release and
> -	 * virtio_driver probe/remove so this object can be freed once no
> -	 * longer in use.
> -	 */
> -	refcount_t refs;
> -
>  	/* What host tells us, plus 2 for header & tailer. */
>  	unsigned int sg_elems;
>  
> @@ -391,43 +384,6 @@ static int virtblk_get_id(struct gendisk *disk, char *id_str)
>  	return err;
>  }
>  
> -static void virtblk_get(struct virtio_blk *vblk)
> -{
> -	refcount_inc(&vblk->refs);
> -}
> -
> -static void virtblk_put(struct virtio_blk *vblk)
> -{
> -	if (refcount_dec_and_test(&vblk->refs)) {
> -		ida_simple_remove(&vd_index_ida, vblk->index);
> -		mutex_destroy(&vblk->vdev_mutex);
> -		kfree(vblk);
> -	}
> -}
> -
> -static int virtblk_open(struct block_device *bd, fmode_t mode)
> -{
> -	struct virtio_blk *vblk = bd->bd_disk->private_data;
> -	int ret = 0;
> -
> -	mutex_lock(&vblk->vdev_mutex);
> -
> -	if (vblk->vdev)
> -		virtblk_get(vblk);
> -	else
> -		ret = -ENXIO;
> -
> -	mutex_unlock(&vblk->vdev_mutex);
> -	return ret;
> -}
> -
> -static void virtblk_release(struct gendisk *disk, fmode_t mode)
> -{
> -	struct virtio_blk *vblk = disk->private_data;
> -
> -	virtblk_put(vblk);
> -}
> -
>  /* We provide getgeo only to please some old bootloader/partitioning tools */
>  static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo)
>  {
> @@ -460,11 +416,19 @@ static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo)
>  	return ret;
>  }
>  
> +static void virtblk_free_disk(struct gendisk *disk)
> +{
> +	struct virtio_blk *vblk = disk->private_data;
> +
> +	ida_simple_remove(&vd_index_ida, vblk->index);
> +	mutex_destroy(&vblk->vdev_mutex);
> +	kfree(vblk);
> +}
> +
>  static const struct block_device_operations virtblk_fops = {
> -	.owner  = THIS_MODULE,
> -	.open = virtblk_open,
> -	.release = virtblk_release,
> -	.getgeo = virtblk_getgeo,
> +	.owner  	= THIS_MODULE,
> +	.getgeo		= virtblk_getgeo,
> +	.free_disk	= virtblk_free_disk,
>  };
>  
>  static int index_to_minor(int index)
> @@ -791,8 +755,6 @@ static int virtblk_probe(struct virtio_device *vdev)
>  		goto out_free_index;
>  	}
>  
> -	/* This reference is dropped in virtblk_remove(). */
> -	refcount_set(&vblk->refs, 1);
>  	mutex_init(&vblk->vdev_mutex);
>  
>  	vblk->vdev = vdev;
> @@ -948,7 +910,13 @@ static int virtblk_probe(struct virtio_device *vdev)
>  	return 0;
>  
>  out_cleanup_disk:
> -	blk_cleanup_disk(vblk->disk);
> +	blk_cleanup_queue(vblk->disk->queue);
> +	blk_mq_free_tag_set(&vblk->tag_set);
> +	vdev->config->del_vqs(vdev);
> +	kfree(vblk->vqs);
> +	put_disk(vblk->disk);
> +	return err;
> +
>  out_free_tags:
>  	blk_mq_free_tag_set(&vblk->tag_set);
>  out_free_vq:
> @@ -970,7 +938,7 @@ static void virtblk_remove(struct virtio_device *vdev)
>  	flush_work(&vblk->config_work);
>  
>  	del_gendisk(vblk->disk);
> -	blk_cleanup_disk(vblk->disk);
> +	blk_cleanup_queue(vblk->disk->queue);
>  	blk_mq_free_tag_set(&vblk->tag_set);
>  
>  	mutex_lock(&vblk->vdev_mutex);
> @@ -986,7 +954,7 @@ static void virtblk_remove(struct virtio_device *vdev)
>  
>  	mutex_unlock(&vblk->vdev_mutex);
>  
> -	virtblk_put(vblk);
> +	put_disk(vblk->disk);
>  }
>  
>  #ifdef CONFIG_PM_SLEEP
> -- 
> 2.30.2
> 
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