linux-kernel - Re: Slab corruption in floppy driver module

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Message-ID: <gity3g14k1.fsf@mx10.gouders.net>
Date:	Sat, 28 Jan 2012 11:53:34 +0100
From:	Dirk Gouders <gouders@...bocholt.fh-gelsenkirchen.de>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Suresh Jayaraman <sjayaraman@...e.com>, Tejun Heo <tj@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, Jens Axboe <axboe@...nel.dk>
Subject: Re: Slab corruption in floppy driver module

Vivek Goyal <vgoyal@...hat.com> writes:

> On Fri, Jan 27, 2012 at 12:30:00PM +0100, Dirk Gouders wrote:
>> Suresh Jayaraman <sjayaraman@...e.com> writes:
>> 
>> > On 01/27/2012 03:18 AM, Dirk Gouders wrote:
>> 
>> [snipped many lines]
>> 
>> >> Probably a rare and uncommon one but it seems that the reloading case on
>> >> a machine that has a floppy controller is a different problem.  To be
>> >> sure I tested the patch on a machine that has a floppy controller and
>> >> when unloading and reloading the floppy module the log messages that I
>> >> attached to a mail earlier in this thread are still generated.
>> >> 
>> >
>> > Yeah, this seems like a different problem. Could you please try enabling
>> > CONFIG_DEBUG_PAGEALLOC and see whether is it pointing to the problem
>> > code while loading/unloading the module?
>> 
>> I enabled the option and it produces just one message during boot but
>> nothing else while unloading/loading the floppy module.
>>
>
> Can you please try following patch and see if it fixes the issue. I could
> reproduce the issue with my virtual machine. The issue seems to be that
> we do not call add_disk() for all the drives/disks but we try to do
> put_disk() on all the disks. Hence running into the issue of putting
> extra reference during module removal.

I tested your patch and it works fine.

There is just a little typo:

floppy: Fix a crash during rmmod

Thanks,

Dirk

> floppy: Fix a crash during rmmmod
>
> floppy driver does not call add_disk() on all the drives hence we don't take
> gendisk reference on request queue for these drives. Don't call put_disk()
> with disk->queue set, otherwise we try to put the reference we never took.
>
> Reported-by: Dirk Gouders <gouders@...bocholt.fh-gelsenkirchen.de> 
> Signed-off-by: Vivek Goyal<vgoyal@...hat.com>
> ---
>  drivers/block/floppy.c |    9 +++++++++
>  1 file changed, 9 insertions(+)
>
> Index: linux-2.6/drivers/block/floppy.c
> ===================================================================
> --- linux-2.6.orig/drivers/block/floppy.c	2012-01-27 14:34:45.000000000 -0500
> +++ linux-2.6/drivers/block/floppy.c	2012-01-27 14:39:13.729861052 -0500
> @@ -4584,6 +4584,15 @@ static void __exit floppy_module_exit(vo
>  			platform_device_unregister(&floppy_device[drive]);
>  		}
>  		blk_cleanup_queue(disks[drive]->queue);
> +
> +		/*
> +		 * These disks have not called add_disk().  Don't put down
> +		 * queue reference in put_disk().
> +		 */
> +		if (!(allowed_drive_mask & (1 << drive)) ||
> +		    fdc_state[FDC(drive)].version == FDC_NONE)
> +			disks[drive]->queue = NULL;
> +
>  		put_disk(disks[drive]);
>  	}
>  
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