[dm-devel] [PATCH 43/44] block: merge struct block_device and struct hd_struct

[Christoph Hellwig]

On Fri, Nov 27, 2020 at 02:19:01PM +0100, Jan Kara wrote:
> The percpu refcount is long gone after the series refactoring...

True.

> > @@ -939,13 +910,13 @@ void blk_request_module(dev_t devt)
> >   */
> >  struct block_device *bdget_disk(struct gendisk *disk, int partno)
> >  {
> > -	struct hd_struct *part;
> >  	struct block_device *bdev = NULL;
> >  
> > -	part = disk_get_part(disk, partno);
> > -	if (part)
> > -		bdev = bdget_part(part);
> > -	disk_put_part(part);
> > +	rcu_read_lock();
> > +	bdev = __disk_get_part(disk, partno);
> > +	if (bdev)
> > +		bdgrab(bdev);
> 
> Again I think you need to accommodate for bdgrab() returning NULL here when
> we race with partition destruction...

For that we need to allow bdgrab to return NULL first, but otherwise
this seems like the right way.