linux-kernel - lockdep: access percpu variable too early

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Date:	Thu, 28 Feb 2013 23:48:00 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: lockdep: access percpu variable too early

Hi,

The percpu variables of 'lockdep_stats' and 'cpu_lock_stat'
may be accessed before percpu area is brought up in case of
CONFIG_DEBUG_LOCKDEP/CONFIG_LOCK_STAT, so these variables
in non-boot CPUs will be initialized incorrectly.

As far as I think of, there are several solutions for the
problem:

	1, just enable 'debug_locks' until percpu area is built
	2, define the two percpu variables in a simple/stupid
	percpu way inside lockdep
	3, clear these two percpu variables of non-boot CPUs
	just after percpu area is built.
	4, ignore the problem

Looks each approache have its own disadvantage, so what
is your opinion on the problem? or better approach?

Thanks,
--
Ming Lei
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