Re: [Nbd] [PATCH 1/6] block: export blkdev_reread_part()

[Christoph Hellwig <hch@...1270...>]

> +/*
> + * This is exported as API for block driver, can be called
> + * with requiring bd_mutex or not.
> + */
> +int __blkdev_reread_part(struct block_device *bdev, bool lock)
>  {
>  	struct gendisk *disk = bdev->bd_disk;
>  	int res;
> @@ -159,12 +163,14 @@ static int blkdev_reread_part(struct block_device *bdev)
>  		return -EINVAL;
>  	if (!capable(CAP_SYS_ADMIN))
>  		return -EACCES;
> -	if (!mutex_trylock(&bdev->bd_mutex))
> +	if (lock && !mutex_trylock(&bdev->bd_mutex))
>  		return -EBUSY;

Please don't add funtions that do conditional locking, instead move
all the code into blkdev_reread_part_nolock, and then wrap it:

int blkdev_reread_part(struct block_device *bdev)
{
	if (!mutex_trylock(&bdev->bd_mutex))
		return -EBUSY;
	blkdev_reread_part_nolock(bdev);
	mutex_unlock(&bdev->bd_mutex);
}

Please also add a lockdep_assert_held to blkdev_reread_part_nolock to
ensure callers actually do hold the lock.