Re: [PATCH 5/9] block: change the refcounting for partitions

[Ming Lei <ming.lei@redhat.com>]

On Thu, Jul 22, 2021 at 09:53:58AM +0200, Christoph Hellwig wrote:
> Instead of acquiring an inode reference on open make sure partitions
> always hold device model references to the disk while alive, and switch
> open to grab only a device model reference to the opened block device.
> If that is a partition the disk reference is transitively held by the
> partition already.
> ---
>  block/partitions/core.c |  9 ++++++-
>  fs/block_dev.c          | 60 ++++++++++++++++-------------------------
>  2 files changed, 31 insertions(+), 38 deletions(-)
> 
> diff --git a/block/partitions/core.c b/block/partitions/core.c
> index 09c58a110a89..4f7a1a9cd544 100644
> --- a/block/partitions/core.c
> +++ b/block/partitions/core.c
> @@ -261,6 +261,7 @@ static void part_release(struct device *dev)
>  {
>  	if (MAJOR(dev->devt) == BLOCK_EXT_MAJOR)
>  		blk_free_ext_minor(MINOR(dev->devt));
> +	put_disk(dev_to_bdev(dev)->bd_disk);
>  	bdput(dev_to_bdev(dev));
>  }
>  
> @@ -349,9 +350,13 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
>  	if (xa_load(&disk->part_tbl, partno))
>  		return ERR_PTR(-EBUSY);
>  
> +	/* ensure we always have a reference to the whole disk */
> +	get_device(disk_to_dev(disk));
> +
> +	err = -ENOMEM;
>  	bdev = bdev_alloc(disk, partno);
>  	if (!bdev)
> -		return ERR_PTR(-ENOMEM);
> +		goto out_put_disk;
>  
>  	bdev->bd_start_sect = start;
>  	bdev_set_nr_sectors(bdev, len);
> @@ -420,6 +425,8 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
>  	device_del(pdev);
>  out_put:
>  	put_device(pdev);
> +out_put_disk:
> +	put_disk(disk);

put_disk() is only needed for failure of bdev_alloc(). Once bdev->bd_device
is initialized, the disk reference will be dropped via part_release().

Thanks,
Ming