linux-kernel - Re: lockdep splat with 3.2-rc2-rt3+

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Message-ID: <20111130083324.GA1632@zhy>
Date:	Wed, 30 Nov 2011 16:33:24 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	John Kacur <jkacur@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Clark Williams <clark.williams@...il.com>,
	RT <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: lockdep splat with 3.2-rc2-rt3+

On Thu, Nov 24, 2011 at 11:50:06PM +0100, John Kacur wrote:
> So, as a little experiment, on v3.2.0-rc2-rt3
> I redefined MAX_LOCKDEP_ENTRIES from 16384UL to 32768UL
> 
> Then from /proc/lockdep_stats
> 
> I got
>  direct dependencies:                 18026 [max: 32768]
> 
> The fact that 18026 is only a little larger than the normal max (by 1642)
> to me is another indication that, this is not a case of something in
> lockdep going out of control that needs to be fixed, but just another
> indication that in some circumstances it would be legitimate to raise
> the value.

Yeah, seems the reason is in RT we have no dedicated softirq-context
anymore, IOW, both process-context and softirq-context are taken as
process-context. That will increase the usage of lockdep entries
because we expand the scope of process-context.

Thanks,
Yong
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