linux-kernel - Re: [PATCH RFC V2 3/6] time: keep track of the pending utc/tai threshold

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Message-ID: <4FC57CAA.3030809@us.ibm.com>
Date:	Tue, 29 May 2012 18:49:30 -0700
From:	John Stultz <johnstul@...ibm.com>
To:	Richard Cochran <richardcochran@...il.com>
CC:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH RFC V2 3/6] time: keep track of the pending utc/tai threshold

On 05/29/2012 06:46 PM, John Stultz wrote:
> On 05/23/2012 11:57 PM, Richard Cochran wrote:
>> On Thu, May 24, 2012 at 08:43:40AM +0200, Richard Cochran wrote:
>>> BTW you can use the program I have been using to test this at
>>>
>>>     git://github.com/richardcochran/leap.git
>> That program exposes another leap second bug, too, I think. It reads
>> the time via adjtimex in a tight loop, optionally sleeping using
>>
>>     clock_nanosleep(CLOCK_MONOTONIC, 0,&ts, NULL);
>>
>> The program does not wake from this call during a leap second. It is
>> my expectation that CLOCK_MONOTONIC should always work. Why doesn't
>> it?
>
> Sorry for being slow here, just got a chance to look at this.
>
> Does the following patch solve this issue for you?

Sorry, attached the wrong patch (that one doesn't build!).

Try this one.

thanks
-john


Make sure we update wall_to_monotonic when adding a leapsecond.
This could otherwise cause discontinuities in CLOCK_MONOTONIC.

Reported-by: Richard Cochran <richardcochran@...il.com>
Signed-off-by: John Stultz <john.stultz@...aro.org>

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 6e46cac..81c76a9 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -962,6 +962,7 @@ static cycle_t logarithmic_accumulation(cycle_t offset, int shift)
  		timekeeper.xtime.tv_sec++;
  		leap = second_overflow(timekeeper.xtime.tv_sec);
  		timekeeper.xtime.tv_sec += leap;
+		timekeeper.wall_to_monotonic.tv_sec -= leap;
  	}

  	/* Accumulate raw time */

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