linux-kernel - Re: [PATCH 0/5 v2] Fixes for leapsecond expiring early ABS_TIME CLOCK

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Message-ID: <CALAqxLXH7RN=Gqv+aTVTGt9-Qo6sv0VzLocwUipaE-7F8pOzTQ@mail.gmail.com>
Date:	Fri, 12 Jun 2015 10:58:42 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Dave Jones <davej@...emonkey.org.uk>,
	John Stultz <john.stultz@...aro.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Prarit Bhargava <prarit@...hat.com>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	Jan Kara <jack@...e.cz>, Jiri Bohac <jbohac@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [PATCH 0/5 v2] Fixes for leapsecond expiring early ABS_TIME
 CLOCK_REALTIME timers

On Fri, Jun 12, 2015 at 7:52 AM, Dave Jones <davej@...emonkey.org.uk> wrote:
> On Thu, Jun 11, 2015 at 03:54:52PM -0700, John Stultz wrote:
>  > So this is a second round at trying to address the issue, trying
>  > to integrate feedback from Ingo and Thomas, trying to simplify
>  > what I can. I've also split out the changes so each can be
>  > more easily reviewed. Its still not tiny, but its simpler.
>  >
>  > This series is against tip/timers/core, and the first patch isn't
>  > strictly related but is a fix that is needed in tip/timers/core.
>  >
>  > As Prarit reported here:
>  > https://lkml.org/lkml/2015/5/27/458
>  >
>  > Since the leapsecond is applied at timer tick time, and not
>  > the actual second edge, ABS_TIME CLOCK_REALTIME timers set for
>  > right after the leapsecond could fire a second early, since
>  > some timers may be expired before we trigger the timekeeping
>  > timer, which then applies the leapsecond.
>  >
>  > Thus this patch series tries to address this issue, including
>  > extending the leap-a-day test to catch this problem, as well
>  > as other relevant fixups I found while working on the code.
>  >
>  > This series has only had limited testing, so I wanted to send
>  > it out for initial review and comment. Folks can grab this tree
>  > via git for testing here:
>  > https://git.linaro.org/people/john.stultz/linux.git dev/early-leap-timer
>
> Any idea how far back this reaches ? Ie, which longterm stable releases
> might be affected by this ?

I suspect all the way back to where hrtimers were introduced and
possibly further.

> (It really creeps me out that we're still changing this code so close
>  to the next leap second event).

Yea. This isn't something I'm suggesting folks deploy for the end of
this month. It likely will be 4.3 material.

thanks
-john
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