linux-kernel - Re: lockdep max numbers (was Re: Crashes during boot on 2.6.30 / 2.6.31-rc, random programs)

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Message-Id: <1246530720.4752.12.camel@laptop>
Date:	Thu, 02 Jul 2009 12:32:00 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Amerigo Wang <xiyou.wangcong@...il.com>
Cc:	Joao Correia <joaomiguelcorreia@...il.com>,
	linux-kernel@...r.kernel.org, Joerg Roedel <joerg.roedel@....com>
Subject: Re: lockdep max numbers (was Re: Crashes during boot on 2.6.30 /
 2.6.31-rc, random programs)

On Thu, 2009-07-02 at 17:31 +0800, Amerigo Wang wrote:
> On Wed, Jul 01, 2009 at 09:30:23PM +0100, Joao Correia wrote:
> >Hello again
> >
> >Looks like this just opened the lid on some other limits. I just hit
> >another thing, which hadn't shown up before i made the changes, but
> >looks like its just another limit thats too low. This one is harder to
> >reproduce tho.
> >
> >Jun 30 21:35:03 hightech kernel: BUG: MAX_LOCKDEP_CHAINS too low!
> >Jun 30 21:35:03 hightech kernel: turning off the locking correctness validator.
> >Jun 30 21:35:03 hightech kernel: Pid: 9379, comm: qemu-kvm Not tainted
> 
> 
> Similar problem...
> 
> Peter? Would like to increase these numbers?

> >2.6.30-wl #3

> >Jun 30 21:35:03 hightech kernel: [<c05d0c66>] debug_dma_map_sg+0xe1/0x147

We recently fixed the dma debug stuff to require less lockdep resources,
Joerg might know if that made it into .30.

> >>>So i dug a little on the source and changed
> >>>
> >>>include/linux/sched.h
> >>>
> >>># define MAX_LOCK_DEPTH 48UL
> >>>
> >>>to
> >>>
> >>># define MAX_LOCK_DEPTH 96UL

> >> Let's Cc: Peter to see if he would like to change this number...
> >>
> >> Peter?

I really don't think we want to raise this, I mean, holding more that 48
locks at the same time is somewhat pushing it, don't you think?

Where do you run into this limit?

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