linux-kernel - Re: Lockdep false positive in sysfs

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Date:	Thu, 3 May 2012 17:30:30 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tejun Heo <tj@...nel.org>
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 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?

Alan Stern

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