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sync_hw_clock() is normally called every 11 minutes when time is synchronized. This issue is that this periodic timer uses the REALTIME clock, so when time moves backwards (the NTP server jumps into the past), the timer expires late. If the timer expires late, which can be days later, the RTC will no longer be updated, which is an issue if the device is abruptly powered OFF during this period. When the device will restart (when powered ON), it will have the date prior to the ADJ_SETOFFSET call. A normal NTP server should not jump in the past like that, but it is possible... Another way of reproducing this issue is to use phc2sys to synchronize the REALTIME clock with, for example, an IRIG timecode with the source always starting at the same date (not synchronized). Also, if the time jump in the future by less than 11 minutes, the RTC may not be updated immediately (minor issue). Consider the following scenario: - Time is synchronized, and sync_hw_clock() was just called (the timer expires in 11 minutes). - A time jump is realized in the future by a couple of minutes. - The time is synchronized again. - Users may expect that RTC to be updated as soon as possible, and not after 11 minutes (for the same reason, if a power loss occurs in this period). Cancel periodic timer on any time jump (ADJ_SETOFFSET) greater than or equal to 1s. The timer will be relaunched at the end of do_adjtimex() if NTP is still considered synced. Otherwise the timer will be relaunched later when NTP is synced. This way, when the time is synchronized again, the RTC is updated after less than 2 seconds. Signed-off-by: Benjamin ROBIN <dev@benjarobin.fr> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/all/20240908140836.203911-1-dev@benjarobin.fr
23 lines
805 B
C
23 lines
805 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_NTP_INTERNAL_H
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#define _LINUX_NTP_INTERNAL_H
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extern void ntp_init(void);
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extern void ntp_clear(void);
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/* Returns how long ticks are at present, in ns / 2^NTP_SCALE_SHIFT. */
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extern u64 ntp_tick_length(void);
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extern ktime_t ntp_get_next_leap(void);
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extern int second_overflow(time64_t secs);
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extern int __do_adjtimex(struct __kernel_timex *txc,
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const struct timespec64 *ts,
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s32 *time_tai, struct audit_ntp_data *ad);
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extern void __hardpps(const struct timespec64 *phase_ts, const struct timespec64 *raw_ts);
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#if defined(CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC)
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extern void ntp_notify_cmos_timer(bool offset_set);
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#else
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static inline void ntp_notify_cmos_timer(bool offset_set) { }
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#endif
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#endif /* _LINUX_NTP_INTERNAL_H */
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