linux-kernel - Re: [PATCH] sysfs: differentiate between locking links and non-links

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Date:	Wed, 10 Feb 2010 10:25:21 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Tejun Heo <tj@...nel.org>
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	Neil Brown <neilb@...e.de>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sysfs: differentiate between locking links and non-links

Tejun Heo <tj@...nel.org> writes:

> On 02/10/2010 05:03 PM, Eric W. Biederman wrote:
>> Tejun Heo <tj@...nel.org> writes:
>> 
>>> Hello,
>>>
>>> On 02/10/2010 11:08 AM, Américo Wang wrote:
>>>> This bug report is new for me. Recently we received lots of sysfs lockdep
>>>> warnings, I am working on a patch to fix all the bogus ones.
>>>>
>>>> However, this one is _not_ similar to the other cases, as you decribed.
>>>> This patch could fix the problem, but not a good fix, IMO. We need more
>>>> work in sysfs layer to fix this kind of things. I will take care of this.
>>>
>>> Can't we just give each s_active lock a separate class?  Would that be
>>> too costly?
>> 
>> When I asked the question earlier I was told that that locking classes
>> require static storage.  Where would that static storage come from?
>
> Maybe I'm glossly misunderstanding it but wouldn't embedding struct
> lockdep_map into sysfs_node as in work_struct do the trick?

In lockdep_init_map there is the following check:

	/*
	 * Sanity check, the lock-class key must be persistent:
	 */
	if (!static_obj(key)) {
		printk("BUG: key %p not in .data!\n", key);
		DEBUG_LOCKS_WARN_ON(1);
		return;
	}

It needs playing with but I think we can embed something in struct
attribute, and simply disallow dynamically allocated instances of
struct attribute.

Eric
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