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

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Message-ID: <20120617173456.GA3684@netboy.at.omicron.at>
Date:	Sun, 17 Jun 2012 19:34:56 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	Jonathan Nieder <jrnieder@...il.com>
Cc:	Ben Hutchings <ben@...adent.org.uk>,
	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 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).
> 
> John, is that bug present in 3.2.y and 3.0.y, too?  Any hints for
> fixing it?

It looks like incrementing the TAI offset was wrong even before 

   6b43ae8a ntp: Fix leap-second hrtimer livelock  v3.4-rc1~44^2~9

The offset should change upon entering state OOP, so something like
the following (untested) patch should fix it for 3.2.9.

Thanks,
Richard

---
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index f6117a4..d7bd953 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -365,6 +365,7 @@ static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
 		break;
 	case TIME_INS:
 		timekeeping_leap_insert(-1);
+		time_tai++;
 		time_state = TIME_OOP;
 		printk(KERN_NOTICE
 			"Clock: inserting leap second 23:59:60 UTC\n");
@@ -379,7 +380,6 @@ static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
 			"Clock: deleting leap second 23:59:59 UTC\n");
 		break;
 	case TIME_OOP:
-		time_tai++;
 		time_state = TIME_WAIT;
 		/* fall through */
 	case TIME_WAIT:
--
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