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

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Message-ID: <20120126180532.GA4077@dhcp-172-17-108-109.mtv.corp.google.com>
Date:	Thu, 26 Jan 2012 10:05:32 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Suresh Jayaraman <sjayaraman@...e.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Dirk Gouders <gouders@...bocholt.fh-gelsenkirchen.de>
Subject: Re: Slab corruption in floppy driver module

Hello,

On Thu, Jan 26, 2012 at 10:04:20AM -0500, Vivek Goyal wrote:
>  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);
> +			/*
> +			 * The request queue reference we took at device
> +			 * creation time has been put by above
> +			 * blk_cleanup_queue(). We have not called add_disk()
> +			 * yet and due to failure calling put_disk(). Put disk
> +			 * will try to put a reference to disk->queue which is
> +			 * taken in add_disk(). As we have not taken that
> +			 * extra reference, putting extra reference down
> +			 * will try to access already freed queue. Clear
> +			 * disk->queue before calling put_disk().
> +			 */
> +			disks[dr]->queue = NULL;

Yeah, this looks correct to me.  It might be better to tone down the
comment a bit tho.  Wouldn't it be sufficient to say put_disk() isn't
paired with add_disk() and will put one extra time?

Thanks.

-- 
tejun
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