linux-kernel - Re: bug in tty ldisc and friends

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Message-ID: <20090616102910.GA11011@elte.hu>
Date:	Tue, 16 Jun 2009 12:29:10 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Joerg Roedel <joerg.roedel@....com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: bug in tty ldisc and friends


* Ingo Molnar <mingo@...e.hu> wrote:

> * Ingo Molnar <mingo@...e.hu> wrote:
> 
> > > On bootup with a totally generic Fedora 11, thinkpad setup 
> > > with the kernel swapped for current git head. Will send the 
> > > .config off list and build it with a 1M entry stack trace 
> > > again.
> > 
> > Nah, dont waste your time on that for now - if it's reproducible 
> > on simple bootup then i will be able to trigger it once i have 
> > your config.
> 
> update: i do trigger it too with your config:
> 
> BUG: MAX_STACK_TRACE_ENTRIES too low!

I have a potential workaround, please disable:

  CONFIG_DMA_API_DEBUG

does it get you below the limit? Here it gives:

 lock-classes:                          549 [max: 8191]
 direct dependencies:                  3288 [max: 16384]
 indirect dependencies:                6753
 all direct dependencies:             49282
 dependency chains:                    3384 [max: 32768]
 dependency chain hlocks:              9901 [max: 163840]
 in-hardirq chains:                      21
 in-softirq chains:                     243
 in-process chains:                    3120
 stack-trace entries:                 81205 [max: 262144]
 combined max dependencies:        16753528

We are now well below the limit for stack-trace entries.

This is something we noticed recently: dma-debug uses a lot of lock 
classes and thus creates a really large lock-graph, depleting the 
reserves quickly.

	Ingo
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