Re: [PATCH 03/19] fs: release anon dev_t in deactivate_locked_super

[Christian Brauner]

> BTW, this part of commit message in 2c18a63b760a is rather confused:
>     Recent rework moved block device closing out of sb->put_super() and into
>     sb->kill_sb() to avoid deadlocks as s_umount is held in put_super() and
>     blkdev_put() can end up taking s_umount again.
> 
> That was *NOT* what a recent rework had done.  Block device closing had never
> been inside ->put_super() - at no point since that (closing, that is) had been
> introduced back in 0.97 ;-)  ->put_super() predates it (0.95c+).

I think the commit message probably just isn't clear enough. The main
block device of a superblock isn't closed in sb->put_super(). That's
always been closed in kill_block_super() after generic_shutdown_super().

But afaict filesystem like ext4 and xfs may have additional block
devices open exclusively and closed them in sb->put_super():

xfs_fs_put_super()
-> xfs_close_devices()
   -> xfs_blkdev_put()
      -> blkdev_put()

ext4_put_super()
-> ext4_blkdev_remove()
   -> blkdev_put()