Subject: Re: [RFC] Fast assurate clock readable from user space and NMI
	handler
From: john stultz <johnstul@us.ibm.com>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Daniel Walker <dwalker@mvista.com>, Ingo Molnar <mingo@elte.hu>,
       mbligh@google.com, linux-kernel@vger.kernel.org,
       Thomas Gleixner <tglx@linutronix.de>
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Date: Tue, 27 Feb 2007 11:40:24 -0800
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On Tue, 2007-02-27 at 14:04 -0500, Mathieu Desnoyers wrote:
> __get_nsec_offset : reads clock->cycle_last. Should be called with
> xtime_lock held. (ok so far, but see below)
> 
> change_clocksource
> clock->cycle_last = now; (non atomic 64 bits update. Not protected by
> any lock ?) -> this would race with __get_nsec_offset ?

Minor nit (it could probably use a comment fixup): its only called from
update_wall_time, which holds xtime_lock. 

> update_wall_time
> Called from timer interrupt. Holds xtime_lock and has a priority higher
> than other interrupts. Other clock->cycle_last protected by
> write_seqlock_irqsave.

-john

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