timekeeping: Try to catch clocksource delta underflows

[cascardo/linux.git] / kernel / time / timekeeping.c

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 657414c..187149b 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -148,6 +148,13 @@ static inline cycle_t timekeeping_get_delta(struct tk_read_base *tkr)
        /* calculate the delta since the last update_wall_time */
        delta = clocksource_delta(cycle_now, tkr->cycle_last, tkr->mask);
 
+       /*
+        * Try to catch underflows by checking if we are seeing small
+        * mask-relative negative values.
+        */
+       if (unlikely((~delta & tkr->mask) < (tkr->mask >> 3)))
+               delta = 0;
+
        /* Cap delta value to the max_cycles values to avoid mult overflows */
        if (unlikely(delta > tkr->clock->max_cycles))
                delta = tkr->clock->max_cycles;