Re: [PATCH 11/20] block: reference struct block_device from struct hd_struct

[Tejun Heo <tj@xxxxxxxxxx>]

Hey, Jan,

On Wed, Nov 25, 2020 at 12:40:44PM +0100, Jan Kara wrote:
> > I don't think this is necessary now that the bdev and inode lifetimes are
> > one. Before, punching out the association early was necessary because we
> > could be in a situation where we can successfully look up a part from idr
> > and then try to pin the associated disk which may already be freed. With the
> > new code, the lookup is through the inode whose lifetime is one and the same
> > with gendisk, so use-after-free isn't possible and __blkdev_get() will
> > reliably reject such open attempts.
> 
> I think the remove_inode_hash() call is actually still needed. Consider a
> situation when the disk is unplugged, gendisk gets destroyed, bdev still
> lives on (e.g. because it is still open). Device gets re-plugged, gendisk
> for the same device number gets created. But we really need new bdev for
> this because from higher level POV this is completely new device. And the
> old bdev needs to live on as long as it is open. So IMO we still need to
> just unhash the inode and leave it lingering in the background.

You're absolutely right. I was only thinking about the lifetime problem
described in the comment. So, it just needs an updated comment there, I
think.

Thanks.

-- 
tejun