linux-kernel - Re: Lockdep false positive in sysfs

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Message-ID: <20120504165232.GB24639@google.com>
Date:	Fri, 4 May 2012 09:52:32 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: Lockdep false positive in sysfs

On Thu, May 03, 2012 at 05:30:30PM -0400, Alan Stern wrote:
> On Fri, 27 Apr 2012, Tejun Heo wrote:
> 
> > > Would it be better to release just the lockdep annotation while
> > > continuing to hold the actual lock, or to really drop the lock?
> > 
> > Just the lockdep annotation, I think.
> 
> This is turning out to be harder than it looked.
> 
> In order to release the lockdep annotation, I need the lockdep_map
> which is stored in the sysfs_dirent structure.  But when the attribute
> method is called, all it is given is a pointer to the attribute itself
> (which contains the lockdep_class_key but not the lockdep_map) and a
> pointer to the corresponding kobject.
> 
> Is there any reasonable way to get from the kobject and the attribute
> to the appropriate sysfs_dirent?  Search through all the groups
> attached to the kobject?  Restrict the new interface so that it can be
> used only by attributes at the kobject's top level (i.e., not in a
> named group)?
> 
> Any suggestions?

Urgh... I can't think of anything pretty.  How about just marking the
attr as "I'm special" and let sysfs code override lockdep annotation?

Thanks.

-- 
tejun
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