3 files changed, 57 insertions, 11 deletions

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 139c4db55f17..c86c940d1de3 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -156,6 +156,7 @@ extern u64 timecounter_cyc2time(struct timecounter *tc,
  * @mult:               cycle to nanosecond multiplier
  * @shift:              cycle to nanosecond divisor (power of two)
  * @max_idle_ns:        max idle time permitted by the clocksource (nsecs)
+ * @maxadj              maximum adjustment value to mult (~11%)
  * @flags:              flags describing special properties
  * @archdata:           arch-specific data
  * @suspend:            suspend function for the clocksource, if necessary
@@ -172,7 +173,7 @@ struct clocksource {
         u32 mult;
         u32 shift;
         u64 max_idle_ns;
-
+        u32 maxadj;
 #ifdef CONFIG_ARCH_CLOCKSOURCE_DATA
         struct arch_clocksource_data archdata;
 #endif
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index cf52fda2e096..cfc65e1eb9fb 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -492,6 +492,22 @@ void clocksource_touch_watchdog(void)
 }
 
 /**
+ * clocksource_max_adjustment- Returns max adjustment amount
+ * @cs:         Pointer to clocksource
+ *
+ */
+static u32 clocksource_max_adjustment(struct clocksource *cs)
+{
+        u64 ret;
+        /*
+         * We won't try to correct for more then 11% adjustments (110,000 ppm),
+         */
+        ret = (u64)cs->mult * 11;
+        do_div(ret,100);
+        return (u32)ret;
+}
+
+/**
  * clocksource_max_deferment - Returns max time the clocksource can be deferred
  * @cs:         Pointer to clocksource
  *
@@ -503,25 +519,28 @@ static u64 clocksource_max_deferment(struct clocksource *cs)
         /*
          * Calculate the maximum number of cycles that we can pass to the
          * cyc2ns function without overflowing a 64-bit signed result. The
-         * maximum number of cycles is equal to ULLONG_MAX/cs->mult which
-         * is equivalent to the below.
-         * max_cycles < (2^63)/cs->mult
-         * max_cycles < 2^(log2((2^63)/cs->mult))
-         * max_cycles < 2^(log2(2^63) - log2(cs->mult))
-         * max_cycles < 2^(63 - log2(cs->mult))
-         * max_cycles < 1 << (63 - log2(cs->mult))
+         * maximum number of cycles is equal to ULLONG_MAX/(cs->mult+cs->maxadj)
+         * which is equivalent to the below.
+         * max_cycles < (2^63)/(cs->mult + cs->maxadj)
+         * max_cycles < 2^(log2((2^63)/(cs->mult + cs->maxadj)))
+         * max_cycles < 2^(log2(2^63) - log2(cs->mult + cs->maxadj))
+         * max_cycles < 2^(63 - log2(cs->mult + cs->maxadj))
+         * max_cycles < 1 << (63 - log2(cs->mult + cs->maxadj))
          * Please note that we add 1 to the result of the log2 to account for
          * any rounding errors, ensure the above inequality is satisfied and
          * no overflow will occur.
          */
-        max_cycles = 1ULL << (63 - (ilog2(cs->mult) + 1));
+        max_cycles = 1ULL << (63 - (ilog2(cs->mult + cs->maxadj) + 1));
 
         /*
          * The actual maximum number of cycles we can defer the clocksource is
          * determined by the minimum of max_cycles and cs->mask.
+         * Note: Here we subtract the maxadj to make sure we don't sleep for
+         * too long if there's a large negative adjustment.
          */
         max_cycles = min_t(u64, max_cycles, (u64) cs->mask);
-        max_nsecs = clocksource_cyc2ns(max_cycles, cs->mult, cs->shift);
+        max_nsecs = clocksource_cyc2ns(max_cycles, cs->mult - cs->maxadj,
+                                        cs->shift);
 
         /*
          * To ensure that the clocksource does not wrap whilst we are idle,
@@ -640,7 +659,6 @@ static void clocksource_enqueue(struct clocksource *cs)
 void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq)
 {
         u64 sec;
-
         /*
          * Calc the maximum number of seconds which we can run before
          * wrapping around. For clocksources which have a mask > 32bit
@@ -661,6 +679,20 @@ void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq)
 
         clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
                                NSEC_PER_SEC / scale, sec * scale);
+
+        /*
+         * for clocksources that have large mults, to avoid overflow.
+         * Since mult may be adjusted by ntp, add an safety extra margin
+         *
+         */
+        cs->maxadj = clocksource_max_adjustment(cs);
+        while ((cs->mult + cs->maxadj < cs->mult)
+                || (cs->mult - cs->maxadj > cs->mult)) {
+                cs->mult >>= 1;
+                cs->shift--;
+                cs->maxadj = clocksource_max_adjustment(cs);
+        }
+
         cs->max_idle_ns = clocksource_max_deferment(cs);
 }
 EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale);
@@ -701,6 +733,12 @@ EXPORT_SYMBOL_GPL(__clocksource_register_scale);
  */
 int clocksource_register(struct clocksource *cs)
 {
+        /* calculate max adjustment for given mult/shift */
+        cs->maxadj = clocksource_max_adjustment(cs);
+        WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
+                "Clocksource %s might overflow on 11%% adjustment\n",
+                cs->name);
+
         /* calculate max idle time permitted for this clocksource */
         cs->max_idle_ns = clocksource_max_deferment(cs);
 
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 025e136f3881..e9f60d311436 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -850,6 +850,13 @@ static void timekeeping_adjust(s64 offset)
         } else /* No adjustment needed */
                 return;
 
+        WARN_ONCE(timekeeper.clock->maxadj &&
+                        (timekeeper.mult + adj > timekeeper.clock->mult +
+                                                timekeeper.clock->maxadj),
+                        "Adjusting %s more then 11%% (%ld vs %ld)\n",
+                        timekeeper.clock->name, (long)timekeeper.mult + adj,
+                        (long)timekeeper.clock->mult +
+                                timekeeper.clock->maxadj);
         /*
          * So the following can be confusing.
          *