linux-kernel - Re: lockdep: BUG: MAX_LOCKDEP

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Message-ID: <20131219154951.GB24658@gmail.com>
Date:	Thu, 19 Dec 2013 16:49:51 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: lockdep: BUG: MAX_LOCKDEP_ENTRIES too low!


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Thu, Dec 19, 2013 at 09:02:14AM -0500, Sasha Levin wrote:
> > On 12/19/2013 05:34 AM, Peter Zijlstra wrote:
> > >On Thu, Dec 19, 2013 at 12:53:56AM -0500, Sasha Levin wrote:
> > >>Hi all,
> > >>
> > >>I think that my bloated kernel managed to create way too many entries in the
> > >>dependency table. If that sounds right, I can send a patch to increase those.
> > >>
> > >>Attached /proc/lock_stat as requested as well.
> > >
> > >/proc/lockdep_stats not lock_stat :-)
> > >
> > >Do you still happen to have that?
> > 
> > Is the BUG message intentional ("Please attach the output of /proc/lock_stat to the bug report")?
> 
> It does? This happened when I wasn't looking..
> 
> Commit 199e371f59d31 did that; and the Changelog fails to mention why or
> what. Ingo, Dave?

Simple oversight I think, should be fixed.

> [...]
>
> One might argue that the validator should be modified to allow lock 
> classes to be reused.  However, if you are tempted to make this 
> argument, first review the code and think through the changes that 
> would be required, keeping in mind that the lock classes to be 
> removed are likely to be linked into the lock-dependency graph.  
> This turns out to be harder to do than to say.

Yes, an append-only data structure was a conscious simplification I 
decided on very early. (It also increases general robustness if your 
data structure can never go away.)

Thanks,

	Ingo
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