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

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Message-ID: <4FF21C88.3060801@us.ibm.com>
Date:	Mon, 02 Jul 2012 15:11:20 -0700
From:	John Stultz <johnstul@...ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
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 07/02/2012 01:53 AM, Thomas Gleixner wrote:
> 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 for the feedback.
I've implemented this, but before I send it out, I'm trying to see if 
there's not a way to change hrtimers so it doesn't keep its own per-cpu 
sense of time.  If I don't sort that out shortly, I'll go ahead and send 
your suggestion out for inclusion so the fix is committed and I can try 
to further improve it afterwards.

thanks
-john

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