linux-kernel - Re: [PATCH v3 2/9] suppress "Device nodeX does not have a release() function" warning

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Date:	Mon, 22 Oct 2012 15:52:24 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	wency@...fujitsu.com
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	rientjes@...gle.com, liuj97@...il.com, len.brown@...el.com,
	benh@...nel.crashing.org, paulus@...ba.org, minchan.kim@...il.com,
	kosaki.motohiro@...fujitsu.com, isimatu.yasuaki@...fujitsu.com,
	Greg KH <greg@...ah.com>
Subject: Re: [PATCH v3 2/9] suppress
 "Device nodeX does not have a release() function" warning

On Fri, 19 Oct 2012 14:46:35 +0800
wency@...fujitsu.com wrote:

> From: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
> 
> When calling unregister_node(), the function shows following message at
> device_release().
> 
> "Device 'node2' does not have a release() function, it is broken and must
> be fixed."
> 
> The reason is node's device struct does not have a release() function.
> 
> So the patch registers node_device_release() to the device's release()
> function for suppressing the warning message. Additionally, the patch adds
> memset() to initialize a node struct into register_node(). Because the node
> struct is part of node_devices[] array and it cannot be freed by
> node_device_release(). So if system reuses the node struct, it has a garbage.
> 
> ...
>
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -252,6 +252,9 @@ static inline void hugetlb_register_node(struct node *node) {}
>  static inline void hugetlb_unregister_node(struct node *node) {}
>  #endif
>  
> +static void node_device_release(struct device *dev)
> +{
> +}
>  
>  /*
>   * register_node - Setup a sysfs device for a node.
> @@ -263,8 +266,11 @@ int register_node(struct node *node, int num, struct node *parent)
>  {
>  	int error;
>  
> +	memset(node, 0, sizeof(*node));
> +
>  	node->dev.id = num;
>  	node->dev.bus = &node_subsys;
> +	node->dev.release = node_device_release;
>  	error = device_register(&node->dev);
>  
>  	if (!error){

Greg won't like that empty ->release function ;)

As you say, this device item does not reside in per-device dynamically
allocated memory - it is part of an externally managed array.

So a proper fix here would be to convert this storage so that it *is*
dynamically allocated on a per-device basis.

Or perhaps we should recognize that the whole kobject
get/put/release-on-last-put model is inappropriate for these objects,
and stop using it entirely.

>From Kosaki's comment, it does sound that we plan to take the first
option: convert to per-device dynamically allocated memory?  If so, I
suggest that we just leave the warning as-is for now, until we fix
things proprely.

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