Re: [PATCH 10/10] md: simplify md_open

[Hannes Reinecke <hare@suse.de>]

On 7/18/22 08:34, Christoph Hellwig wrote:
> Now that devices are on the all_mddevs list until the gendisk is freed,
> there can't be any duplicates.  Remove the global list lookup and just
> grab a reference.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   drivers/md/md.c | 42 +++++++++++++++---------------------------
>   1 file changed, 15 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 08cf21ad4c2d7..9b1e61b4bac8b 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -7785,45 +7785,33 @@ static int md_set_read_only(struct block_device *bdev, bool ro)
>   
>   static int md_open(struct block_device *bdev, fmode_t mode)
>   {
> -	/*
> -	 * Succeed if we can lock the mddev, which confirms that
> -	 * it isn't being stopped right now.
> -	 */
> -	struct mddev *mddev = mddev_find(bdev->bd_dev);
> +	struct mddev *mddev;
>   	int err;
>   
> +	spin_lock(&all_mddevs_lock);
> +	mddev = mddev_get(bdev->bd_disk->private_data);
> +	spin_unlock(&all_mddevs_lock);
>   	if (!mddev)
>   		return -ENODEV;
>   
> -	if (mddev->gendisk != bdev->bd_disk) {
> -		/* we are racing with mddev_put which is discarding this
> -		 * bd_disk.
> -		 */
> -		mddev_put(mddev);
> -		/* Wait until bdev->bd_disk is definitely gone */
> -		if (work_pending(&mddev->del_work))
> -			flush_workqueue(md_misc_wq);
> -		return -EBUSY;
> -	}
> -	BUG_ON(mddev != bdev->bd_disk->private_data);
> -
> -	if ((err = mutex_lock_interruptible(&mddev->open_mutex)))
> +	err = mutex_lock_interruptible(&mddev->open_mutex);
> +	if (err)
>   		goto out;
>   
> -	if (test_bit(MD_CLOSING, &mddev->flags)) {
> -		mutex_unlock(&mddev->open_mutex);
> -		err = -ENODEV;
> -		goto out;
> -	}
> +	err = -ENODEV;
> +	if (test_bit(MD_CLOSING, &mddev->flags))
> +		goto out_unlock;
>   
> -	err = 0;
>   	atomic_inc(&mddev->openers);
>   	mutex_unlock(&mddev->open_mutex);
>   
>   	bdev_check_media_change(bdev);
> - out:
> -	if (err)
> -		mddev_put(mddev);
> +	return 0;
> +
> +out_unlock:
> +	mutex_unlock(&mddev->open_mutex);
> +out:
> +	mddev_put(mddev);
>   	return err;
>   }
>   

Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes