[PATCH 37/44] block: switch partition lookup to use struct block_device

[Jan Kara]

On Thu 26-11-20 14:04:15, Christoph Hellwig wrote:
>  struct hd_struct *disk_get_part(struct gendisk *disk, int partno)
>  {
> -	struct hd_struct *part;
> +	struct block_device *part;
>  
>  	rcu_read_lock();
>  	part = __disk_get_part(disk, partno);
> -	if (part)
> -		get_device(part_to_dev(part));
> -	rcu_read_unlock();
> +	if (!part) {
> +		rcu_read_unlock();
> +		return NULL;
> +	}
>  
> -	return part;
> +	get_device(part_to_dev(part->bd_part));
> +	rcu_read_unlock();
> +	return part->bd_part;
>  }

This is not directly related to this particular patch but I'm wondering:
What prevents say del_gendisk() from racing with disk_get_part(), so that
delete_partition() is called just after we fetched 'part' pointer and the
last 'part' kobject ref is dropped before disk_get_part() calls
get_device()? I don't see anything preventing that and so we'd hand out
'part' that is soon to be freed (after RCU grace period expires).

								Honza

-- 
Jan Kara <jack at suse.com>
SUSE Labs, CR