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Date: Tue, 26 May 2009 14:15:52 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: linux-kernel@vger.kernel.org, greg@kroah.com,
       Kay Sievers <kay.sievers@vrfy.org>, Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH] devres: WARN() and return, don't crash on device_del()
 of uninitialized device
Message-Id: <20090526141552.507f8821.akpm@linux-foundation.org>
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On Mon, 25 May 2009 16:53:31 +1000
Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> I just debugged an obscure crash caused by a device_del() of a all NULL'd
> out struct device (in usb-serial) and found that a patch like this one would
> have saved me time (in addition to improved chances of a bug report from
> users hitting similar driver bugs).
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> ---
> 
>  drivers/base/devres.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> --- linux-work.orig/drivers/base/devres.c	2009-05-25 16:43:46.000000000 +1000
> +++ linux-work/drivers/base/devres.c	2009-05-25 16:46:36.000000000 +1000
> @@ -428,6 +428,11 @@ int devres_release_all(struct device *de
>  {
>  	unsigned long flags;
>  
> +	/* Looks like an uninitialized device structure */
> +	if (dev->devres_head.next == NULL) {
> +		WARN(1);
> +		return -ENODEV;
> +	}
>  	spin_lock_irqsave(&dev->devres_lock, flags);
>  	return release_nodes(dev, dev->devres_head.next, &dev->devres_head,
>  			     flags);

This could be coded a little more neatly as:

	/* Looks like an uninitialized device structure */
	if (WARN_ON(dev->devres_head.next == NULL))
		return -ENODEV;