From: John Stultz <john.stultz@xxxxxxxxxx> 3.4.113-rc1 review patch. If anyone has any objections, please let me know. ------------------ commit 833f32d763028c1bb371c64f457788b933773b3e upstream. Currently, leapsecond adjustments are done at tick time. As a result, the leapsecond was applied at the first timer tick *after* the leapsecond (~1-10ms late depending on HZ), rather then exactly on the second edge. This was in part historical from back when we were always tick based, but correcting this since has been avoided since it adds extra conditional checks in the gettime fastpath, which has performance overhead. However, it was recently pointed out that ABS_TIME CLOCK_REALTIME timers set for right after the leapsecond could fire a second early, since some timers may be expired before we trigger the timekeeping timer, which then applies the leapsecond. This isn't quite as bad as it sounds, since behaviorally it is similar to what is possible w/ ntpd made leapsecond adjustments done w/o using the kernel discipline. Where due to latencies, timers may fire just prior to the settimeofday call. (Also, one should note that all applications using CLOCK_REALTIME timers should always be careful, since they are prone to quirks from settimeofday() disturbances.) However, the purpose of having the kernel do the leap adjustment is to avoid such latencies, so I think this is worth fixing. So in order to properly keep those timers from firing a second early, this patch modifies the ntp and timekeeping logic so that we keep enough state so that the update_base_offsets_now accessor, which provides the hrtimer core the current time, can check and apply the leapsecond adjustment on the second edge. This prevents the hrtimer core from expiring timers too early. This patch does not modify any other time read path, so no additional overhead is incurred. However, this also means that the leap-second continues to be applied at tick time for all other read-paths. Apologies to Richard Cochran, who pushed for similar changes years ago, which I resisted due to the concerns about the performance overhead. While I suspect this isn't extremely critical, folks who care about strict leap-second correctness will likely want to watch this. Potentially a -stable candidate eventually. Originally-suggested-by: Richard Cochran <richardcochran@xxxxxxxxx> Reported-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> Reported-by: Prarit Bhargava <prarit@xxxxxxxxxx> Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx> Cc: Richard Cochran <richardcochran@xxxxxxxxx> Cc: Jan Kara <jack@xxxxxxx> Cc: Jiri Bohac <jbohac@xxxxxxx> Cc: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Link: http://lkml.kernel.org/r/1434063297-28657-4-git-send-email-john.stultz@xxxxxxxxxx Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> [Yadi: Move do_adjtimex to timekeeping.c and solve context issues] Signed-off-by: Hu <yadi.hu@xxxxxxxxxxxxx> Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx> --- kernel/time/ntp.c | 45 ++++++++++++++++++++++++++++++++++++++------- kernel/time/timekeeping.c | 37 +++++++++++++++++++++++++++++++++++-- 2 files changed, 73 insertions(+), 9 deletions(-) diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c index e32587e..ea8d82e 100644 --- a/kernel/time/ntp.c +++ b/kernel/time/ntp.c @@ -34,6 +34,7 @@ unsigned long tick_nsec; static u64 tick_length; static u64 tick_length_base; +#define SECS_PER_DAY 86400 #define MAX_TICKADJ 500LL /* usecs */ #define MAX_TICKADJ_SCALED \ (((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ) @@ -78,6 +79,9 @@ static long time_adjust; /* constant (boot-param configurable) NTP tick adjustment (upscaled) */ static s64 ntp_tick_adj; +/* second value of the next pending leapsecond, or KTIME_MAX if no leap */ +static s64 ntp_next_leap_sec = KTIME_MAX; + #ifdef CONFIG_NTP_PPS /* @@ -354,6 +358,8 @@ void ntp_clear(void) time_maxerror = NTP_PHASE_LIMIT; time_esterror = NTP_PHASE_LIMIT; + ntp_next_leap_sec = KTIME_MAX; + ntp_update_frequency(); tick_length = tick_length_base; @@ -377,6 +383,21 @@ u64 ntp_tick_length(void) return ret; } +/** + * ntp_get_next_leap - Returns the next leapsecond in CLOCK_REALTIME ktime_t + * + * Provides the time of the next leapsecond against CLOCK_REALTIME in + * a ktime_t format. Returns KTIME_MAX if no leapsecond is pending. + */ +ktime_t ntp_get_next_leap(void) +{ + ktime_t ret; + + if ((time_state == TIME_INS) && (time_status & STA_INS)) + return ktime_set(ntp_next_leap_sec, 0); + ret.tv64 = KTIME_MAX; + return ret; +} /* * this routine handles the overflow of the microsecond field @@ -403,15 +424,21 @@ int second_overflow(unsigned long secs) */ switch (time_state) { case TIME_OK: - if (time_status & STA_INS) + if (time_status & STA_INS) { time_state = TIME_INS; - else if (time_status & STA_DEL) + ntp_next_leap_sec = secs + SECS_PER_DAY - + (secs % SECS_PER_DAY); + } else if (time_status & STA_DEL) { time_state = TIME_DEL; + ntp_next_leap_sec = secs + SECS_PER_DAY - + ((secs+1) % SECS_PER_DAY); + } break; case TIME_INS: - if (!(time_status & STA_INS)) + if (!(time_status & STA_INS)) { + ntp_next_leap_sec = KTIME_MAX; time_state = TIME_OK; - else if (secs % 86400 == 0) { + } else if (secs % SECS_PER_DAY == 0) { leap = -1; time_state = TIME_OOP; time_tai++; @@ -420,10 +447,12 @@ int second_overflow(unsigned long secs) } break; case TIME_DEL: - if (!(time_status & STA_DEL)) + if (!(time_status & STA_DEL)) { + ntp_next_leap_sec = KTIME_MAX; time_state = TIME_OK; - else if ((secs + 1) % 86400 == 0) { + } else if ((secs + 1) % SECS_PER_DAY == 0) { leap = 1; + ntp_next_leap_sec = KTIME_MAX; time_tai--; time_state = TIME_WAIT; printk(KERN_NOTICE @@ -431,6 +460,7 @@ int second_overflow(unsigned long secs) } break; case TIME_OOP: + ntp_next_leap_sec = KTIME_MAX; time_state = TIME_WAIT; break; @@ -549,6 +579,7 @@ static inline void process_adj_status(struct timex *txc, struct timespec *ts) if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) { time_state = TIME_OK; time_status = STA_UNSYNC; + ntp_next_leap_sec = KTIME_MAX; /* restart PPS frequency calibration */ pps_reset_freq_interval(); } @@ -619,7 +650,7 @@ static inline void process_adjtimex_modes(struct timex *txc, struct timespec *ts * adjtimex mainly allows reading (and writing, if superuser) of * kernel time-keeping variables. used by xntpd. */ -int do_adjtimex(struct timex *txc) +int __do_adjtimex(struct timex *txc) { struct timespec ts; int result; diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 32f0cb8..a72f63e 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -21,6 +21,9 @@ #include <linux/tick.h> #include <linux/stop_machine.h> +extern ktime_t ntp_get_next_leap(void); +extern int __do_adjtimex(struct timex *); + /* Structure holding internal timekeeping values. */ struct timekeeper { /* Current clocksource used for timekeeping. */ @@ -30,6 +33,8 @@ struct timekeeper { /* The shift value of the current clocksource. */ int shift; + /* CLOCK_MONOTONIC time value of a pending leap-second*/ + ktime_t next_leap_ktime; /* Number of clock cycles in one NTP interval. */ cycle_t cycle_interval; /* Number of clock shifted nano seconds in one NTP interval. */ @@ -186,6 +191,17 @@ static void update_rt_offset(void) timekeeper.offs_real = timespec_to_ktime(tmp); } +/* + * tk_update_leap_state - helper to update the next_leap_ktime + */ +static inline void tk_update_leap_state(struct timekeeper *tk) +{ + tk->next_leap_ktime = ntp_get_next_leap(); + if (tk->next_leap_ktime.tv64 != KTIME_MAX) + /* Convert to monotonic time */ + tk->next_leap_ktime = ktime_sub(tk->next_leap_ktime, tk->offs_real); +} + /* must hold write on timekeeper.lock */ static void timekeeping_update(bool clearntp) { @@ -193,6 +209,7 @@ static void timekeeping_update(bool clearntp) timekeeper.ntp_error = 0; ntp_clear(); } + tk_update_leap_state(&timekeeper); update_rt_offset(); update_vsyscall(&timekeeper.xtime, &timekeeper.wall_to_monotonic, timekeeper.clock, timekeeper.mult); @@ -1329,10 +1346,16 @@ ktime_t ktime_get_update_offsets(ktime_t *offs_real, ktime_t *offs_boot) *offs_real = timekeeper.offs_real; *offs_boot = timekeeper.offs_boot; + + now = ktime_add_ns(ktime_set(secs, 0), nsecs); + now = ktime_sub(now, *offs_real); + + /* Handle leapsecond insertion adjustments */ + if (unlikely(now.tv64 >= timekeeper.next_leap_ktime.tv64)) + *offs_real = ktime_sub(timekeeper.offs_real, ktime_set(1, 0)); + } while (read_seqretry(&timekeeper.lock, seq)); - now = ktime_add_ns(ktime_set(secs, 0), nsecs); - now = ktime_sub(now, *offs_real); return now; } #endif @@ -1354,6 +1377,16 @@ ktime_t ktime_get_monotonic_offset(void) } EXPORT_SYMBOL_GPL(ktime_get_monotonic_offset); +/* + * do_adjtimex() - Accessor function to NTP __do_adjtimex function + */ +int do_adjtimex(struct timex *txc) +{ + int ret; + ret = __do_adjtimex(txc); + tk_update_leap_state(&timekeeper); + return ret; +} /** * xtime_update() - advances the timekeeping infrastructure -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html