time, Fix setting of hardware clock in NTP code (84e345e4) · Commits · 戴 / test

At init time, if the system time is "warped" forward in warp_clock() it will differ from the hardware clock by sys_tz.tz_minuteswest. This time difference is not taken into account when ntp updates the hardware clock, and this causes the system time to jump forward by this offset every reboot. The kernel must take this offset into account when writing the system time to the hardware clock in the ntp code. This patch adds persistent_clock_is_local which indicates that an offset has been applied in warp_clock() and accounts for the "warp" before writing the hardware clock. x86 does not have this problem as rtc writes are software limited to a +/-15 minute window relative to the current rtc time. Other arches, such as powerpc, however do a full synchronization of the system time to the rtc and will see this problem. [v2]: generated against tip/timers/core Signed-off-by:

Prarit Bhargava <prarit@redhat.com> Cc: John Stultz <john.stultz@linaro.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by:

John Stultz <john.stultz@linaro.org>

include/linux/time.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -128,6 +128,7 @@ static inline bool has_persistent_clock(void)

		extern void read_persistent_clock(struct timespec *ts);
		extern void read_boot_clock(struct timespec *ts);
		extern int persistent_clock_is_local;
		extern int update_persistent_clock(struct timespec now);
		void timekeeping_init(void);
		extern int timekeeping_suspended;

kernel/time.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -114,6 +114,12 @@ SYSCALL_DEFINE2(gettimeofday, struct timeval __user *, tv,
		return 0;
		}

		/*
		* Indicates if there is an offset between the system clock and the hardware
		* clock/persistent clock/rtc.
		*/
		int persistent_clock_is_local;

		/*
		* Adjust the time obtained from the CMOS to be UTC time instead of
		* local time.
		@@ -135,6 +141,8 @@ static inline void warp_clock(void)
		struct timespec adjust;

		adjust = current_kernel_time();
		if (sys_tz.tz_minuteswest != 0)
		persistent_clock_is_local = 1;
		adjust.tv_sec += sys_tz.tz_minuteswest * 60;
		do_settimeofday(&adjust);
		}

kernel/time/ntp.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -511,13 +511,17 @@ static void sync_cmos_clock(struct work_struct *work)

		getnstimeofday(&now);
		if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2) {
		struct timespec adjust = now;

		fail = -ENODEV;
		if (persistent_clock_is_local)
		adjust.tv_sec -= (sys_tz.tz_minuteswest * 60);
		#ifdef CONFIG_GENERIC_CMOS_UPDATE
		fail = update_persistent_clock(now);
		fail = update_persistent_clock(adjust);
		#endif
		#ifdef CONFIG_RTC_SYSTOHC
		if (fail == -ENODEV)
		fail = rtc_set_ntp_time(now);
		fail = rtc_set_ntp_time(adjust);
		#endif
		}

Admin message