linux-kernel - Re: [RFC][PATCH 0/3] configfs: Make nested default groups lockdep-friendly

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Message-ID: <20080520222702.GJ26609@mail.oracle.com>
Date:	Tue, 20 May 2008 15:27:02 -0700
From:	Joel Becker <Joel.Becker@...cle.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Louis Rilling <Louis.Rilling@...labs.com>,
	linux-kernel@...r.kernel.org, ocfs2-devel@....oracle.com
Subject: Re: [RFC][PATCH 0/3] configfs: Make nested default groups
	lockdep-friendly

On Tue, May 20, 2008 at 03:13:41PM -0700, Arjan van de Ven wrote:
> > 	Louis, what about sticking the recursion level on
> > configfs_dirent?  That is, you could add sd->s_level and then use it
> > when needed.  THis would hopefully avoid having to pass the level as
> > an argument to every function.  Then we can go back to your original
> > scheme.  If they recurse too much and hit the lockdep limit, just
> > rewind everything and return -ELOOP.
> 
> you can also make a new lockdep key for each level... not pretty but it
> works

	I think that's what we're talking about here.  The toplevel is
I_MUTEX_PARENT, then each child has a class of (I_MUTEX_CHILD + depth),
where depth is the value of s_level.  His original try passed depth
everywhere.  I'm asking him to attach it to the configfs_dirent so that
the code stays readable.  We run into a depth limit at
(MAX_LOCKDEP_SUBCLASS - I_MUTEX_PARENT - 1 == 5), which I think is
probably sane.
	Do you mean something else?  Perhaps not starting from
I_MUTEX_PARENT/CHILD and instead creating CONFIGFS_MUTEX_XXX?

Joel

-- 

"Copy from one, it's plagiarism; copy from two, it's research."
        - Wilson Mizner

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@...cle.com
Phone: (650) 506-8127
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