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Date:   Thu, 26 Nov 2020 09:16:50 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Tejun Heo <tj@kernel.org>
Cc:     Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        Josef Bacik <josef@toxicpanda.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
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Subject: Re: [PATCH 25/45] block: reference struct block_device from struct
 hd_struct
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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).