linux-kernel - Re: [PATCH 1/2] [RFC] Fix clock_was_set so it is safe to call from atomic

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Date:	Mon, 2 Jul 2012 10:53:08 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	John Stultz <johnstul@...ibm.com>
cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Prarit Bhargava <prarit@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] [RFC] Fix clock_was_set so it is safe to call from
 atomic

On Sun, 1 Jul 2012, John Stultz wrote:

> NOTE:This is a prerequisite patch that's required to
> address the widely observed leap-second related futex/hrtimer
> issues.
> 
> Currently clock_was_set() is unsafe to be called from atomic
> context, as it calls on_each_cpu(). This causes problems when
> we need to adjust the time from update_wall_time().
> 
> To fix this, introduce a work_struct so if we're in_atomic,
> we can schedule work to do the necessary update after we're
> out of the atomic section.

Shouldn't we queue a timer_list timer with expiry time jiffies + 0
instead. We can call on_each_cpu() from softirq context. And that
ensures that the update happens right away, while a scheduled work
might be delayed arbitrary long.

Thanks,

	tglx
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