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

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Date:	Wed, 10 Feb 2010 15:05:44 -0800
From:	Greg KH <gregkh@...e.de>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Américo Wang <xiyou.wangcong@...il.com>,
	Neil Brown <neilb@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sysfs: differentiate between locking links and
 non-links

On Wed, Feb 10, 2010 at 10:25:21AM -0800, Eric W. Biederman wrote:
> 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.

I think some code dynamically creates attributes today, as this has
never been a restriction.

So I don't know if this is going to work :(

thanks,

greg k-h
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