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

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Date:	Tue, 14 Aug 2012 16:00:32 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Ben Hutchings <ben@...adent.org.uk>
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,
	Stanislaw Gruszka <sgruszka@...hat.com>
Subject: Re: [PATCH v3 3/6] floppy: avoid leaking extra reference to queue on
 do_floppy_init error handling

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, which is then
> dropped by disk_release().  But if a disk is destroyed without being
> registered through add_disk() (or if add_disk() fails at the first
> hurdle) then we have a reference imbalance.
> 
> Use the GENHD_FL_UP flag to tell whether this extra reference has been
> added.  Remove the incomplete workaround from the floppy driver.
> 

Checking for GENHD_FL_UP to represent whether we took a reference on the
disk->queue or not sounds reasonable. 

Thanks
Vivek
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