linux-kernel - Re: [PATCH v3 3/6] floppy: avoid leaking extra reference to queue on do_floppy

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Message-ID: <1344954487.824.203.camel@deadeye.wl.decadent.org.uk>
Date:	Tue, 14 Aug 2012 15:28:07 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
Cc:	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>,
	Jens Axboe <axboe@...nel.dk>, Jiri Kosina <jkosina@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH v3 3/6] floppy: avoid leaking extra reference to queue
 on do_floppy_init error handling

On Tue, 2012-08-14 at 11:03 +0200, Stanislaw Gruszka wrote:
> On Tue, Aug 14, 2012 at 04:20:39AM +0100, Ben Hutchings wrote:
> > On Mon, 2012-08-13 at 15:16 -0300, Herton Ronaldo Krzesinski wrote:
> > > After commit 3f9a5aa ("floppy: Cleanup disk->queue before caling
> > > put_disk() if add_disk() was never called"), if something fails in the
> > > add_disk loop, we unconditionally set disks[dr]->queue to NULL. But
> > > that's wrong, since we may have succesfully done an add_disk on some of
> > > the drives previously in the loop, and in this case we would end up with
> > > an extra reference to the disks[dr]->queue.
> > > 
> > > Add a new global array to mark "registered" disks, and use that to check
> > > if we did an add_disk on one of the disks already. Using an array to
> > > track added disks also will help to simplify/cleanup code later, as
> > > suggested by Vivek Goyal.
> > [...]
> > 
> > It's totally ridiculous that a driver should have to do this.  Any
> > registered disk should have the GENHD_FL_UP flag set... so why can't
> > genhd check it?  It doesn't look like floppy is the only driver affected
> > by this problem, either.  So I suggest the following general fix
> > (untested):
> > 
> > ---
> > Subject: genhd: Make put_disk() safe for disks that have not been registered
> > 
> > Since commit 9f53d2f ('block: fix __blkdev_get and add_disk race
> > condition'), add_disk() adds a reference to disk->queue,
> 
> I do not see this? Commit 9f53d2fe insert disk_alloc_events() to add_disk(),
> but disk_alloc_events() function does not get any reference to disk->queue,
> I missed something?

Sorry, not sure why I pointed to that one.  The reference should of
course be to:

commit 523e1d399ce0e23bec562abe2b2f8d297af81161
Author: Tejun Heo <tj@...nel.org>
Date:   Wed Oct 19 14:31:07 2011 +0200

    block: make gendisk hold a reference to its queue

Ben.

-- 
Ben Hutchings
I say we take off; nuke the site from orbit.  It's the only way to be sure.

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