linux-kernel - Re: [PATCH -stable] ntp: Correct TAI offset during leap second

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Date:	Sun, 01 Jul 2012 02:28:18 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	Jonathan Nieder <jrnieder@...il.com>,
	John Stultz <johnstul@...ibm.com>, stable@...r.kernel.org,
	Sasha Levin <levinsasha928@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dave Jones <davej@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -stable]  ntp: Correct TAI offset during leap second

On Mon, 2012-06-18 at 14:55 +0100, Ben Hutchings wrote:
> On Sun, 2012-06-17 at 19:34 +0200, Richard Cochran wrote:
> > On Sun, Jun 17, 2012 at 11:47:51AM -0500, Jonathan Nieder wrote:
> > > Ben Hutchings wrote:
> > > > On Fri, 2012-06-15 at 11:56 -0700, John Stultz wrote:
> > > 
> > > >> commit dd48d708ff3e917f6d6b6c2b696c3f18c019feed upstream.
> > > [...]
> > > > This doesn't apply to 3.2.y, unsurprisingly.  Let me know if there are
> > > > any urgent leap second fixes that will be needed there.
> > > 
> > > 6b43ae8a619d (ntp: Fix leap-second hrtimer livelock) sounds important,
> > > but the patch depends on bd3312681f69 (ntp: Add ntp_lock to replace
> > > xtime_locking) which does not have a commit message explaining its
> > > purpose (and that patch in turn depends on ea7cf49a7633).
> 
> If I understand the commit message for 6b43ae8a619d correctly, the
> livelock results from ntp_lock and xtime_lock being acquired in opposite
> orders in two threads.  Which means it wasn't possible before ntp_lock
> was introduced in bd3312681f69.
[...]

Apparently some other livelock was possible, though I was unable to
reproduce it myself.  Some proportion of systems running 2.6.32 or 3.2
(not sure about the intermediate stable-supported versions) are reported
to have locked up, either in adjtimex or during the leap second.

I understand that we might not have so long to wait for the next leap
second, so if anyone understands what fixes are still needed in stable
updates I would really appreciate that.

Ben.

-- 
Ben Hutchings
If you seem to know what you are doing, you'll be given more to do.

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