Re: [PATCH v2] ataflop: remove ataflop_probe_lock mutex

Luis Chamberlain
2021-10-21T16:21:07Z

On Thu, Oct 21, 2021 at 09:20:06AM -0700, Luis Chamberlain wrote:
> On Sun, Oct 17, 2021 at 11:09:47AM +0900, Tetsuo Handa wrote:
> > Commit bf9c0538e485b591 ("ataflop: use a separate gendisk for each media
> > format") introduced ataflop_probe_lock mutex, but forgot to unlock the
> > mutex when atari_floppy_init() (i.e. module loading) succeeded. This will
> > result in double lock deadlock if ataflop_probe() is called. Also,
> > unregister_blkdev() must not be called from atari_floppy_init() with
> > ataflop_probe_lock held when atari_floppy_init() failed, for
> > ataflop_probe() waits for ataflop_probe_lock with major_names_lock held
> > (i.e. AB-BA deadlock).
> >
> > __register_blkdev() needs to be called last in order to avoid calling
> > ataflop_probe() when atari_floppy_init() is about to fail, for memory for
> > completing already-started ataflop_probe() safely will be released as soon
> > as atari_floppy_init() released ataflop_probe_lock mutex.
> >
> > As with commit 8b52d8be86d72308 ("loop: reorder loop_exit"),
> > unregister_blkdev() needs to be called first in order to avoid calling
> > ataflop_alloc_disk() from ataflop_probe() after del_gendisk() from
> > atari_floppy_exit().
> >
> > By relocating __register_blkdev() / unregister_blkdev() as explained above,
> > we can remove ataflop_probe_lock mutex, for probe function and __exit
> > function are serialized by major_names_lock mutex.
> >
> > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > Fixes: bf9c0538e485b591 ("ataflop: use a separate gendisk for each media format")
>
> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>

I should note though that this does not apply to linux-next, I rebased
it and will send a rebased version on my v3 series of my last patch set
for add_disk error handling work().

Luis