2 files changed, 13 insertions, 1 deletions

diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h
index f7ac48d2edf5..e9660e52dc09 100644
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -90,6 +90,15 @@ struct timekeeper {
         u64                     xtime_interval;
         s64                     xtime_remainder;
         u32                     raw_interval;
+        /* The ntp_tick_length() value currently being used.
+         * This cached copy ensures we consistently apply the tick
+         * length for an entire tick, as ntp_tick_length may change
+         * mid-tick, and we don't want to apply that new value to
+         * the tick in progress.
+         */
+        u64                     ntp_tick;
+        /* Difference between accumulated time and NTP time in ntp
+         * shifted nano seconds. */
         s64                     ntp_error;
         u32                     ntp_error_shift;
         u32                     ntp_err_mult;
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 43c706a7a728..f36b02838a47 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -171,6 +171,7 @@ static void tk_setup_internals(struct timekeeper *tk, struct clocksource *clock)
 
         tk->ntp_error = 0;
         tk->ntp_error_shift = NTP_SCALE_SHIFT - clock->shift;
+        tk->ntp_tick = ntpinterval << tk->ntp_error_shift;
 
         /*
          * The timekeeper keeps its own mult values for the currently
@@ -1352,6 +1353,8 @@ static __always_inline void timekeeping_freqadjust(struct timekeeper *tk,
         if (tk->ntp_err_mult)
                 xinterval -= tk->cycle_interval;
 
+        tk->ntp_tick = ntp_tick_length();
+
         /* Calculate current error per tick */
         tick_error = ntp_tick_length() >> tk->ntp_error_shift;
         tick_error -= (xinterval + tk->xtime_remainder);
@@ -1497,7 +1500,7 @@ static cycle_t logarithmic_accumulation(struct timekeeper *tk, cycle_t offset,
         tk->raw_time.tv_nsec = raw_nsecs;
 
         /* Accumulate error between NTP and clock interval */
-        tk->ntp_error += ntp_tick_length() << shift;
+        tk->ntp_error += tk->ntp_tick << shift;
         tk->ntp_error -= (tk->xtime_interval + tk->xtime_remainder) <<
                                                 (tk->ntp_error_shift + shift);