Merge branch 'timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  ntp: Clamp PLL update interval

1 files changed, 11 insertions, 3 deletions

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index c63116863a80..d2321891538f 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -149,10 +149,18 @@ static void ntp_update_offset(long offset)
         time_reftime = get_seconds();
 
         offset64    = offset;
-        freq_adj    = (offset64 * secs) <<
-                        (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));
+        freq_adj    = ntp_update_offset_fll(offset64, secs);
 
-        freq_adj    += ntp_update_offset_fll(offset64, secs);
+        /*
+         * Clamp update interval to reduce PLL gain with low
+         * sampling rate (e.g. intermittent network connection)
+         * to avoid instability.
+         */
+        if (unlikely(secs > 1 << (SHIFT_PLL + 1 + time_constant)))
+                secs = 1 << (SHIFT_PLL + 1 + time_constant);
+
+        freq_adj    += (offset64 * secs) <<
+                        (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));
 
         freq_adj    = min(freq_adj + time_freq, MAXFREQ_SCALED);