linux-kernel - Re: [PATCH 08/20 -v5] initialize the clock source to jiffies clock.

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Date:	Wed, 23 Jan 2008 08:40:32 -0800
From:	Tim Bird <tim.bird@...sony.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sam Ravnborg <sam@...nborg.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	John Stultz <johnstul@...ibm.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH 08/20 -v5] initialize the clock source to jiffies clock.

Steven Rostedt wrote:
> The latency tracer can call clocksource_read very early in bootup and
> before the clock source variable has been initialized. This results in a
> crash at boot up (even before earlyprintk is initialized). Since the
> clock->read variable points to NULL.
> 
> This patch simply initializes the clock to use clocksource_jiffies, so
> that any early user of clocksource_read will not crash.

There's a similar problem with reads of sched_clock() too early
on some architectures.  This problem reminds me of a fix I need
to re-send to the ARM mailing list.  That aside, I heartily recommend
applying this patch, whether the rest of this system gets mainlined
or not.

FWIW:
Acked-by: Tim Bird <tim.bird@...sony.com>

 -- Tim


=============================
Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Corporation of America
=============================

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