linux-kernel - Re: [PATCH 1/3] Increase lockdep limits: MAX_STACK_TRACE

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Date:	Tue, 07 Jul 2009 17:55:01 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Joao Correia <joaomiguelcorreia@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Américo Wang <xiyou.wangcong@...il.com>
Subject: Re: [PATCH 1/3] Increase lockdep limits: MAX_STACK_TRACE_ENTRIES

On Tue, 2009-07-07 at 16:50 +0100, Joao Correia wrote:

> >> Yes. Anything 2.6.31 forward triggers this immediatly during init
> >> process, at random places.
> >
> > Not on my machines it doesn't.. so I suspect its something weird in
> > your .config or maybe due to some hardware you have that I don't that
> > triggers different drivers or somesuch.
> 
> I am not the only one reporting this, and it happens, for example,
> with a stock .config from a Fedora 11 install.
> 
> It may, of course, be a funny driver interaction yes, but other than
> stripping the box piece by piece, how would one go about debugging
> this otherwise?

One thing to do is stare (or share) at the output
of /proc/lockdep_chains and see if there's some particularly large
chains in there, or many of the same name or something.

/proc/lockdep_stats might also be interesting, mine reads like:

[root@...eron ~]# cat /proc/lockdep_stats
 lock-classes:                          641 [max: 8191]
 direct dependencies:                  3794 [max: 16384]
 indirect dependencies:                7557
 all direct dependencies:             73254
 dependency chains:                    3716 [max: 32768]
 dependency chain hlocks:             10167 [max: 163840]
 in-hardirq chains:                      21
 in-softirq chains:                     353
 in-process chains:                    3342
 stack-trace entries:                 91035 [max: 262144]
 combined max dependencies:        26035284
 hardirq-safe locks:                     28
 hardirq-unsafe locks:                  460
 softirq-safe locks:                    114
 softirq-unsafe locks:                  373
 irq-safe locks:                        123
 irq-unsafe locks:                      460
 hardirq-read-safe locks:                 0
 hardirq-read-unsafe locks:              45
 softirq-read-safe locks:                 8
 softirq-read-unsafe locks:              39
 irq-read-safe locks:                     8
 irq-read-unsafe locks:                  45
 uncategorized locks:                   106
 unused locks:                            1
 max locking depth:                      14
 max recursion depth:                    10
 debug_locks:                             1


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