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

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Date:	Tue, 16 Jun 2009 12:45:59 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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


* Joerg Roedel <joerg.roedel@....com> wrote:

> On Tue, Jun 16, 2009 at 12:29:10PM +0200, Ingo Molnar wrote:
> > 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.
> 
> Is this considered a problem? I increased the hash-size to 1024 
> for performance reasons (== 1024 spin_locks). But if it hurts to 
> much in other places this can be reverted.

Lockdep running out of stack slots is a problem - but we dont want 
to revert your patch: lockdep is really a helper to development, it 
just observes, never hinders changes like that.

The good news is that the (untested) patch i sent should largely 
solve this problem and reduce dma-debug's lockdep footprint by a 
factor of 1024.

Reverting your change would only be a workaround really.

	Ingo
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