linux-kernel - Re: [ 02/70] floppy: Cleanup disk->queue before caling put_disk() if add

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Date:	Wed, 08 Aug 2012 01:40:25 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Vivek Goyal <vgoyal@...hat.com>,
	Dirk Gouders <gouders@...bocholt.fh-gelsenkirchen.de>,
	Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [ 02/70] floppy: Cleanup disk->queue before caling put_disk()
 if add_disk() was never called

On Tue, 2012-08-07 at 19:49 -0300, Herton Ronaldo Krzesinski wrote:
> On Tue, Aug 07, 2012 at 04:27:57AM +0100, Ben Hutchings wrote:
> > 3.2-stable review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Vivek Goyal <vgoyal@...hat.com>
> > 
> > commit 3f9a5aabd0a9fe0e0cd308506f48963d79169aa7 upstream.
> > 
> > add_disk() takes gendisk reference on request queue. If driver failed during
> > initialization and never called add_disk() then that extra reference is not
> > taken. That reference is put in put_disk(). floppy driver allocates the
> > disk, allocates queue, sets disk->queue and then relizes that floppy
> > controller is not present. It tries to tear down everything and tries to
> > put a reference down in put_disk() which was never taken.
> > 
> > In such error cases cleanup disk->queue before calling put_disk() so that
> > we never try to put down a reference which was never taken in first place.
> > 
> > Reported-and-tested-by: Suresh Jayaraman <sjayaraman@...e.com>
> > Tested-by: Dirk Gouders <gouders@...bocholt.fh-gelsenkirchen.de>
> > Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
> > Acked-by: Tejun Heo <tj@...nel.org>
> > Signed-off-by: Jens Axboe <axboe@...nel.dk>
> > Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
> > ---
> >  drivers/block/floppy.c |    8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
> > index 510fb10..401ba78 100644
> > --- a/drivers/block/floppy.c
> > +++ b/drivers/block/floppy.c
> > @@ -4368,8 +4368,14 @@ out_unreg_blkdev:
> >  out_put_disk:
> >  	while (dr--) {
> >  		del_timer_sync(&motor_off_timer[dr]);
> > -		if (disks[dr]->queue)
> > +		if (disks[dr]->queue) {
> >  			blk_cleanup_queue(disks[dr]->queue);
> > +			/*
> > +			 * put_disk() is not paired with add_disk() and
> > +			 * will put queue reference one extra time. fix it.
> > +			 */
> > +			disks[dr]->queue = NULL;
> > +		}
> >  		put_disk(disks[dr]);
> >  	}
> >  	return err;
> 
> I was taking a look at this, and noticed some issues with the error
> handling:
> * missing cleanup (put_disk) if blk_init_queue fails, dr is decremented
>   first in the error handling loop
> * if something fails in the add_disk loop, there is no cleanup of
>   previous iterations in the error handling.
> * if (disks[dr]->queue) check is bogus, when reaching there for each dr
>   should exist an queue allocated, and it doesn't take into account
>   iterations where add_disk wasn't done, if failure happens in add_disk
>   loop.
> * floppy_module_exit doesn't reset queue pointer if add_disk wasn't
>   done.

I agree with this analysis.

> I think the more complete diff below (not build tested) is needed, comments?
[...]

There are several off-by-one errors, and 'drive_cnt' is not a
particularly clear variable name (alongside 'dr' and 'drive'), but I
think this is on the right track.

Anyway, do you agree that the patch under review does fix *a* bug and
doesn't introduce a regression?

Ben.

-- 
Ben Hutchings
Theory and practice are closer in theory than in practice.
                                - John Levine, moderator of comp.compilers

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