linux-kernel - Re: [PATCH] time, ntp: Do not update time

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Message-ID: <20150218173852.GB31353@midget.suse.cz>
Date:	Wed, 18 Feb 2015 18:38:52 +0100
From:	Jiri Bohac <jbohac@...e.cz>
To:	Jiri Bohac <jbohac@...e.cz>
Cc:	John Stultz <john.stultz@...aro.org>,
	Roman Zippel <zippel@...ux-m68k.org>,
	Prarit Bhargava <prarit@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Miroslav Lichvar <mlichvar@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] time, ntp: Do not update time_state in middle of leap
 second [v3]

On Wed, Feb 18, 2015 at 06:14:04PM +0100, Jiri Bohac wrote:
> I think the only real problem occurs when the adjtimex is called in the
> the TIME_OOP state 

... or the TIME_WAIT state ... 

> with STA_PLL cleared  _and_ STA_INS set.
> In this case the state machine is reset to TIME_OK but goes back
> to TIME_INS on the next second_overflow, potentially causing
> another false leap second to be inserted on the following
> midnight.
> 
> The state machine is meant to only go back to TIME_INS once STA_INS is
> cleared and then set again - this is what the TIME_WAIT state is
> for.
> 
> In fact, I don't see a reason why the STA_PLL -> !STA_PLL transition should 
> ever set the time_state to TIME_OK.
> - When the STA_INS/STA_DEL flag is removed from the status, the state
>   machine will end up in TIME_OK from any state.
> - When STA_INS/STA_DEL is set in
>   the status, the state mchine will transition from TIME_OK to
>   TIME_INS/TIME_DEL anyway.
> 
> I think the "time_status = TIME_OK" should be just dropped.
> 
> It has been added by eea83d896e318bda54be2d2770d2c5d6668d11db
> (ntp: NTP4 user space bits update) and it's not clear why.
> Roman?

-- 
Jiri Bohac <jbohac@...e.cz>
SUSE Labs, SUSE CZ

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