linux-kernel - Re: MAX_LOCKDEP_SUBCLASSES too low in 2.6.23-rc7-mm1

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Message-ID: <20070924165903.GA24220@Krystal>
Date:	Mon, 24 Sep 2007 12:59:03 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...hat.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, Dave Hansen <haveblue@...ibm.com>,
	Alexey Dobriyan <adobriyan@...ru>
Subject: Re: MAX_LOCKDEP_SUBCLASSES too low in 2.6.23-rc7-mm1

* Peter Zijlstra (peterz@...radead.org) wrote:
> On Mon, 24 Sep 2007 12:03:58 -0400 Mathieu Desnoyers
> <mathieu.desnoyers@...ymtl.ca> wrote:
> 
> > Hi Ingo,
> > 
> > I got the following printk when booting 2.6.23-rc7-mm1 :
> > 
> > BUG: MAX_LOCKDEP_SUBCLASSES too low!
> > turning off the locking correctness validator.
> > 
> > Is it known/correct situation ?
> 
> Known, bug in r/o mounts code:
> 
> > static void lock_and_coalesce_cpu_mnt_writer_counts(void)
> > {
> > 	int cpu;
> > 	struct mnt_writer *cpu_writer;
> > 
> > 	for_each_possible_cpu(cpu) {
> > 		cpu_writer = &per_cpu(mnt_writers, cpu);
> > 		spin_lock_nested(&cpu_writer->lock, 42);
> > 		                                   ^^^^
> > 

How could the Ultimate Answer be wrong ? ;)

Cheers,

Mathieu

> > What the heck is going on? Given that MAX_LOCKDEP_SUBCLASSES is only 8,
> > this reliably turns off lockdep at boot.

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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