Message-ID: <1341106098.4852.64.camel@deadeye.wl.decadent.org.uk>
Subject: Re: [PATCH -stable]  ntp: Correct TAI offset during leap second
From: Ben Hutchings <ben@decadent.org.uk>
To: Richard Cochran <richardcochran@gmail.com>
Cc: Jonathan Nieder <jrnieder@gmail.com>, John Stultz <johnstul@us.ibm.com>,
        stable@vger.kernel.org, Sasha Levin <levinsasha928@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>, Dave Jones <davej@redhat.com>,
        lkml <linux-kernel@vger.kernel.org>
Date: Sun, 01 Jul 2012 02:28:18 +0100
In-Reply-To: <1340027711.9372.29.camel@deadeye.wl.decadent.org.uk>
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	 <20120617164751.GJ12429@burratino>
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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:
> > >=20
> > > >> 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.
> > >=20
> > > 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).
>=20
> 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.

--=20
Ben Hutchings
If you seem to know what you are doing, you'll be given more to do.

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