From 35b603f8a78b0bd51566db277c4f7b56b3ff6bac Mon Sep 17 00:00:00 2001 From: Benjamin ROBIN Date: Sun, 8 Sep 2024 16:08:36 +0200 Subject: [PATCH] ntp: Make sure RTC is synchronized when time goes backwards 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 Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/all/20240908140836.203911-1-dev@benjarobin.fr --- kernel/time/ntp.c | 10 +++++++++- kernel/time/ntp_internal.h | 4 ++-- kernel/time/timekeeping.c | 4 +++- 3 files changed, 14 insertions(+), 4 deletions(-) diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c index 8d2dd214ec68..802b336f4b8c 100644 --- a/kernel/time/ntp.c +++ b/kernel/time/ntp.c @@ -660,8 +660,16 @@ rearm: sched_sync_hw_clock(offset_nsec, res != 0); } -void ntp_notify_cmos_timer(void) +void ntp_notify_cmos_timer(bool offset_set) { + /* + * If the time jumped (using ADJ_SETOFFSET) cancels sync timer, + * which may have been running if the time was synchronized + * prior to the ADJ_SETOFFSET call. + */ + if (offset_set) + hrtimer_cancel(&sync_hrtimer); + /* * When the work is currently executed but has not yet the timer * rearmed this queues the work immediately again. No big issue, diff --git a/kernel/time/ntp_internal.h b/kernel/time/ntp_internal.h index 23d1b74c3065..5a633dce9057 100644 --- a/kernel/time/ntp_internal.h +++ b/kernel/time/ntp_internal.h @@ -14,9 +14,9 @@ extern int __do_adjtimex(struct __kernel_timex *txc, extern void __hardpps(const struct timespec64 *phase_ts, const struct timespec64 *raw_ts); #if defined(CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC) -extern void ntp_notify_cmos_timer(void); +extern void ntp_notify_cmos_timer(bool offset_set); #else -static inline void ntp_notify_cmos_timer(void) { } +static inline void ntp_notify_cmos_timer(bool offset_set) { } #endif #endif /* _LINUX_NTP_INTERNAL_H */ diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 5391e4167d60..7e6f409bf311 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -2553,6 +2553,7 @@ int do_adjtimex(struct __kernel_timex *txc) { struct timekeeper *tk = &tk_core.timekeeper; struct audit_ntp_data ad; + bool offset_set = false; bool clock_set = false; struct timespec64 ts; unsigned long flags; @@ -2575,6 +2576,7 @@ int do_adjtimex(struct __kernel_timex *txc) if (ret) return ret; + offset_set = delta.tv_sec != 0; audit_tk_injoffset(delta); } @@ -2608,7 +2610,7 @@ int do_adjtimex(struct __kernel_timex *txc) if (clock_set) clock_was_set(CLOCK_SET_WALL); - ntp_notify_cmos_timer(); + ntp_notify_cmos_timer(offset_set); return ret; }