time: Fix timeekeping_get_ns overflow on 32bit systems (ec145bab) · Commits · 戴 / test

Daniel Lezcano reported seeing multi-second stalls from keyboard input on his T61 laptop when NOHZ and CPU_IDLE were enabled on a 32bit kernel. He bisected the problem down to commit ("time: Condense timekeeper.xtime into xtime_sec"). After reproducing this issue, I narrowed the problem down to the fact that timekeeping_get_ns() returns a 64bit nsec value that hasn't been accumulated. In some cases this value was being then stored in timespec.tv_nsec (which is a long). On 32bit systems, with idle times larger then 4 seconds (or less, depending on the value of xtime_nsec), the returned nsec value would overflow 32bits. This limited kept time from increasing, causing timers to not expire. The fix is to make sure we don't directly store the result of timekeeping_get_ns() into a tv_nsec field, instead using a 64bit nsec value which can then be added into the timespec via timespec_add_ns(). Reported-and-bisected-by:

Daniel Lezcano <daniel.lezcano@linaro.org> Tested-by:

Daniel Lezcano <daniel.lezcano@linaro.org> Signed-off-by:

John Stultz <john.stultz@linaro.org> Acked-by:

Prarit Bhargava <prarit@redhat.com> Cc: Richard Cochran <richardcochran@gmail.com> Link: http://lkml.kernel.org/r/1347405963-35715-1-git-send-email-john.stultz@linaro.org Signed-off-by:

Ingo Molnar <mingo@kernel.org>

kernel/time/timekeeping.c

+12 −7

Original line number	Diff line number	Diff line
		@@ -303,10 +303,11 @@ void getnstimeofday(struct timespec *ts)
		seq = read_seqbegin(&tk->lock);

		ts->tv_sec = tk->xtime_sec;
		ts->tv_nsec = timekeeping_get_ns(tk);
		nsecs = timekeeping_get_ns(tk);

		} while (read_seqretry(&tk->lock, seq));

		ts->tv_nsec = 0;
		timespec_add_ns(ts, nsecs);
		}
		EXPORT_SYMBOL(getnstimeofday);
		@@ -345,6 +346,7 @@ void ktime_get_ts(struct timespec *ts)
		{
		struct timekeeper *tk = &timekeeper;
		struct timespec tomono;
		s64 nsec;
		unsigned int seq;

		WARN_ON(timekeeping_suspended);
		@@ -352,13 +354,14 @@ void ktime_get_ts(struct timespec *ts)
		do {
		seq = read_seqbegin(&tk->lock);
		ts->tv_sec = tk->xtime_sec;
		ts->tv_nsec = timekeeping_get_ns(tk);
		nsec = timekeeping_get_ns(tk);
		tomono = tk->wall_to_monotonic;

		} while (read_seqretry(&tk->lock, seq));

		set_normalized_timespec(ts, ts->tv_sec + tomono.tv_sec,
		ts->tv_nsec + tomono.tv_nsec);
		ts->tv_sec += tomono.tv_sec;
		ts->tv_nsec = 0;
		timespec_add_ns(ts, nsec + tomono.tv_nsec);
		}
		EXPORT_SYMBOL_GPL(ktime_get_ts);

		@@ -1244,6 +1247,7 @@ void get_monotonic_boottime(struct timespec *ts)
		{
		struct timekeeper *tk = &timekeeper;
		struct timespec tomono, sleep;
		s64 nsec;
		unsigned int seq;

		WARN_ON(timekeeping_suspended);
		@@ -1251,14 +1255,15 @@ void get_monotonic_boottime(struct timespec *ts)
		do {
		seq = read_seqbegin(&tk->lock);
		ts->tv_sec = tk->xtime_sec;
		ts->tv_nsec = timekeeping_get_ns(tk);
		nsec = timekeeping_get_ns(tk);
		tomono = tk->wall_to_monotonic;
		sleep = tk->total_sleep_time;

		} while (read_seqretry(&tk->lock, seq));

		set_normalized_timespec(ts, ts->tv_sec + tomono.tv_sec + sleep.tv_sec,
		ts->tv_nsec + tomono.tv_nsec + sleep.tv_nsec);
		ts->tv_sec += tomono.tv_sec + sleep.tv_sec;
		ts->tv_nsec = 0;
		timespec_add_ns(ts, nsec + tomono.tv_nsec + sleep.tv_nsec);
		}
		EXPORT_SYMBOL_GPL(get_monotonic_boottime);

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