linux-kernel - Re: configfs, dlm

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Date:	Thu, 11 Dec 2008 09:34:37 -0800
From:	Joel Becker <Joel.Becker@...cle.com>
To:	Steven Whitehouse <swhiteho@...hat.com>,
	linux-kernel@...r.kernel.org, cluster-devel@...hat.com
Subject: Re: configfs, dlm_controld & lockdep

On Thu, Dec 11, 2008 at 03:44:41PM +0100, Louis Rilling wrote:
> These warnings are known issues. This results from a lack of lockdep annotations
> in configfs. I must admit that I started to send patches for that a few months
> ago, and then could not find time to finish this work.
> 
> The problem is a bit harder than just playing with I_MUTEX_CHILD, I_MUTEX_PARENT
> and I_MUTEX_NORMAL, since configfs recursively locks variable numbers
> (this can go to as many as the depth of the whole configfs tree) of
> config_group inodes during operations like mkdir(), rmdir(), and depend_item().
> 
> I was working on two kinds of solutions:
> 1) insert lockdep_off()/lockdep_on() at the places of recursion,
> 2) separate default groups inode mutex classes according to their depth under
> the created group they belong to.
> 
> People tend to reject any proposition like 1), but IIRC Joel was tending to
> accept it.
> 
> Solution 2) does not work for depend_item(). This needs to rework the locking
> scheme of depend_item() by removing the variable lock recursion depth, and I
> think that it's doable thanks to the configfs_dirent_lock.
> 	Joel, what do you think about this?

	I've been waiting for your patch for (1).  I am wary of the (2)
approach.  Not because it wouldn't work for mkdir(2) - I think it would.
But rmdir(2) has the same recursive locking, with far more importance
(live objects), and would print the same error.

Joel

-- 

Life's Little Instruction Book #267

	"Lie on your back and look at the stars."

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