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>

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 580a350..fc08eb1 100644 (file)
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -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) {