1 files changed, 50 insertions, 12 deletions

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index e0980f0d9a0..8f77da18fef 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -494,6 +494,22 @@ 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
  *
@@ -505,25 +521,28 @@ 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,
@@ -531,7 +550,7 @@ static u64 clocksource_max_deferment(struct clocksource *cs)
          * note a margin of 12.5% is used because this can be computed with
          * a shift, versus say 10% which would require division.
          */
-        return max_nsecs - (max_nsecs >> 5);
+        return max_nsecs - (max_nsecs >> 3);
 }
 
 #ifndef CONFIG_ARCH_USES_GETTIMEOFFSET
@@ -642,7 +661,6 @@ 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
@@ -653,7 +671,7 @@ void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq)
          * ~ 0.06ppm granularity for NTP. We apply the same 12.5%
          * margin as we do in clocksource_max_deferment()
          */
-        sec = (cs->mask - (cs->mask >> 5));
+        sec = (cs->mask - (cs->mask >> 3));
         do_div(sec, freq);
         do_div(sec, scale);
         if (!sec)
@@ -663,6 +681,20 @@ 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);
@@ -703,6 +735,12 @@ 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);