[PATCH 25/45] block: reference struct block_device from struct hd_struct

[Christoph Hellwig]

On Wed, Nov 25, 2020 at 03:20:23PM -0500, Tejun Heo wrote:
> Agreed. It'd be nice to replace the stale comment.

I've updated the comment.

> > Jan added lookup_sem in commit 56c0908c855afbb to prevent a three way
> > race between del_gendisk and blkdev_open due to the weird bdev vs
> > gendisk lifetime rules.  None of that can happen with the new lookup
> > scheme.
> 
> Understood. I think it'd be worthwhile to note that in the commit log.

So after the idea of just holding a disk reference from each bdev did
not work out very well I've reworked this a bit, and lookup_sem stays,
but becomes global to protect the disk lookup (similar to the previous
global bdev_map_lock).