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SubjectRe: [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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