From mboxrd@z Thu Jan  1 00:00:00 1970
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
Subject: Re: [PATCH v4 03/17] sched_clock: Use an hrtimer instead of timer
Date: Mon, 22 Jul 2013 20:07:17 +0100
Message-ID: <20130722190717.GO24642@n2100.arm.linux.org.uk>
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To: Stephen Boyd <sboyd@codeaurora.org>
Cc: John Stultz <john.stultz@linaro.org>, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Thomas Gleixner <tglx@linutronix.de>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Christopher Covington <cov@codeaurora.org>
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On Mon, Jul 22, 2013 at 11:58:47AM -0700, Stephen Boyd wrote:
> On 07/22/13 11:45, Stephen Boyd wrote:
> > Hmm. Is it too early to use hrtimers? Moving the hrtimer_start() into
> > sched_clock_register() also causes the same crash.
> 
> Yes that seems to be the problem. The vexpress board is setting up the
> sched_clock in setup_arch() (via v2m_init_early) which runs before
> hrtimers_init(). I've only tested this on boards that setup the timer in
> the time_init() callback which runs after hrtimers_init(). Your patch
> should be fine, although it would be nice if we didn't have callers
> setting up the sched_clock so early.

However, it _is_ the correct place to do it, as I've repeatedly stated.
The reason for this is that the scheduler will have already read from
sched_clock() by the time you get to timer_init() to seed its idea of
the start time for PID0 - again, as I've explained multiple times.