Commit 10dd31a7 authored Feb 22, 2009 by Ingo Molnar

time: ntp: fix bug in ntp_update_offset() & do_adjtimex()



Impact: change (fix) the way the NTP PLL seconds offset is initialized/tracked

Fix a bug and do a micro-optimization:

When PLL is enabled we do not reset time_reftime. If the PLL
was off for a long time (for example after bootup), this is
arguably the wrong thing to do.

We already had a hack for the common boot-time case in
ntp_update_offset(), in form of:

	if (unlikely(time_status & STA_FREQHOLD || time_reftime == 0))
 		secs = 0;

But the update delta should be reset later on too - not just when
the PLL is enabled for the first time after bootup.

So do it on !STA_PLL -> STA_PLL transitions.

This changes behavior, as previously if ntpd was disabled for
a long time and we restarted it, we'd run from that last update,
with a very large delta.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent c7986acb

kernel/time/ntp.c

+8 −1

Original line number	Diff line number	Diff line
		@@ -142,7 +142,7 @@ static void ntp_update_offset(long offset)
		* and in which mode (PLL or FLL).
		*/
		secs = xtime.tv_sec - time_reftime;
		if (unlikely(time_status & STA_FREQHOLD \|\| time_reftime == 0))
		if (unlikely(time_status & STA_FREQHOLD))
		secs = 0;

		time_reftime = xtime.tv_sec;
		@@ -394,6 +394,13 @@ int do_adjtimex(struct timex *txc)
		}
		/* only set allowed bits */
		time_status &= STA_RONLY;
		/*
		* If we turn on PLL adjustments then reset the
		* reference time to current time.
		*/
		if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
		time_reftime = xtime.tv_sec;

		time_status \|= txc->status & ~STA_RONLY;

		switch (time_state) {

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