diff options
| -rw-r--r-- | kernel/time/timekeeping.c | 64 |
1 files changed, 57 insertions, 7 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 187149be83ea..892f6cbf1e67 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -119,6 +119,20 @@ static inline void tk_update_sleep_time(struct timekeeper *tk, ktime_t delta) } #ifdef CONFIG_DEBUG_TIMEKEEPING +#define WARNING_FREQ (HZ*300) /* 5 minute rate-limiting */ +/* + * These simple flag variables are managed + * without locks, which is racy, but ok since + * we don't really care about being super + * precise about how many events were seen, + * just that a problem was observed. + */ +static int timekeeping_underflow_seen; +static int timekeeping_overflow_seen; + +/* last_warning is only modified under the timekeeping lock */ +static long timekeeping_last_warning; + static void timekeeping_check_update(struct timekeeper *tk, cycle_t offset) { @@ -136,28 +150,64 @@ static void timekeeping_check_update(struct timekeeper *tk, cycle_t offset) printk_deferred(" timekeeping: Your kernel is still fine, but is feeling a bit nervous\n"); } } + + if (timekeeping_underflow_seen) { + if (jiffies - timekeeping_last_warning > WARNING_FREQ) { + printk_deferred("WARNING: Underflow in clocksource '%s' observed, time update ignored.\n", name); + printk_deferred(" Please report this, consider using a different clocksource, if possible.\n"); + printk_deferred(" Your kernel is probably still fine.\n"); + timekeeping_last_warning = jiffies; + } + timekeeping_underflow_seen = 0; + } + + if (timekeeping_overflow_seen) { + if (jiffies - timekeeping_last_warning > WARNING_FREQ) { + printk_deferred("WARNING: Overflow in clocksource '%s' observed, time update capped.\n", name); + printk_deferred(" Please report this, consider using a different clocksource, if possible.\n"); + printk_deferred(" Your kernel is probably still fine.\n"); + timekeeping_last_warning = jiffies; + } + timekeeping_overflow_seen = 0; + } } static inline cycle_t timekeeping_get_delta(struct tk_read_base *tkr) { - cycle_t cycle_now, delta; + cycle_t now, last, mask, max, delta; + unsigned int seq; - /* read clocksource */ - cycle_now = tkr->read(tkr->clock); + /* + * Since we're called holding a seqlock, the data may shift + * under us while we're doing the calculation. This can cause + * false positives, since we'd note a problem but throw the + * results away. So nest another seqlock here to atomically + * grab the points we are checking with. + */ + do { + seq = read_seqcount_begin(&tk_core.seq); + now = tkr->read(tkr->clock); + last = tkr->cycle_last; + mask = tkr->mask; + max = tkr->clock->max_cycles; + } while (read_seqcount_retry(&tk_core.seq, seq)); - /* calculate the delta since the last update_wall_time */ - delta = clocksource_delta(cycle_now, tkr->cycle_last, tkr->mask); + delta = clocksource_delta(now, last, mask); /* * Try to catch underflows by checking if we are seeing small * mask-relative negative values. */ - if (unlikely((~delta & tkr->mask) < (tkr->mask >> 3))) + if (unlikely((~delta & mask) < (mask >> 3))) { + timekeeping_underflow_seen = 1; delta = 0; + } /* Cap delta value to the max_cycles values to avoid mult overflows */ - if (unlikely(delta > tkr->clock->max_cycles)) + if (unlikely(delta > max)) { + timekeeping_overflow_seen = 1; delta = tkr->clock->max_cycles; + } return delta; } |