Re: [PATCH 12/13] loop: remove lo_refcount and avoid lo_mutex in ->open / ->release

[Christoph Hellwig <hch@lst.de>]

On Mon, Mar 28, 2022 at 10:30:45AM +0200, Jan Kara wrote:
> On Fri 25-03-22 17:23:31, Christoph Hellwig wrote:
> > On Fri, Mar 25, 2022 at 07:54:15PM +0900, Tetsuo Handa wrote:
> > > > But for now I'd really prefer to stop moving the goalpost further and
> > > > further.
> > > 
> > > Then, why not kill this code?
> > 
> > I think we should eventually do that, and I've indeed tested a patch
> > that is only cosmetically different.  I wasn't really convinced we
> > should do it in this series, but if there is consensus that we should
> > do it now I can respin the series with a patch like this included.
> 
> I'd defer it to a separate patchset. Because as much as the change to
> disallow LOOP_CLR_FD ioctl for used loop device makes sense, I'm not sure
> there isn't some framework using loop devices somewhere which relies on
> this just getting magically translated to setting LO_AUTOCLEAR flag. So IMO
> this has a big potential of userspace visible regression and as such I'd
> prefer doing it separately from the bugfixes.

At least my idea would not be to disallow LOOP_CLR_FD on a used block
devices as that would go back to the udev problems before Dave turned
it into a magic LO_AUTOCLEAR.  But to remove the lo_refcnt check
entirely, as loop_clr_fd now is safe against concurrent users - it
has to anyway as there can be other users even without an open.

> 
> 								Honza
> -- 
> Jan Kara <jack@suse.com>
> SUSE Labs, CR
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