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authorJohn Stultz <john.stultz@linaro.org>2015-06-11 15:54:56 -0700
committerThomas Gleixner <tglx@linutronix.de>2015-06-12 11:15:49 +0200
commit96efdcf2d080687e041b0353c604b708546689fd (patch)
tree6303e6876a6ac67a9186d44e44bd497f96def781
parent833f32d763028c1bb371c64f457788b933773b3e (diff)
ntp: Do leapsecond adjustment in adjtimex read path
Since the leapsecond is applied at tick-time, this means there is a small window of time at the start of a leap-second where we cross into the next second before applying the leap. This patch modified adjtimex so that the leap-second is applied on the second edge. Providing more correct leapsecond behavior. This does make it so that adjtimex()'s returned time values can be inconsistent with time values read from gettimeofday() or clock_gettime(CLOCK_REALTIME,...) for a brief period of one tick at the leapsecond. However, those other interfaces do not provide the TIME_OOP time_state return that adjtimex() provides, which allows the leapsecond to be properly represented. They instead only see a time discontinuity, and cannot tell the first 23:59:59 from the repeated 23:59:59 leap second. This seems like a reasonable tradeoff given clock_gettime() / gettimeofday() cannot properly represent a leapsecond, and users likely care more about performance, while folks who are using adjtimex() more likely care about leap-second correctness. Signed-off-by: John Stultz <john.stultz@linaro.org> Cc: Prarit Bhargava <prarit@redhat.com> Cc: Daniel Bristot de Oliveira <bristot@redhat.com> Cc: Richard Cochran <richardcochran@gmail.com> Cc: Jan Kara <jack@suse.cz> Cc: Jiri Bohac <jbohac@suse.cz> Cc: Ingo Molnar <mingo@kernel.org> Link: http://lkml.kernel.org/r/1434063297-28657-5-git-send-email-john.stultz@linaro.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
-rw-r--r--kernel/time/ntp.c18
1 files changed, 18 insertions, 0 deletions
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 033743e3647a..fb4d98c7fd43 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -740,6 +740,24 @@ int __do_adjtimex(struct timex *txc, struct timespec64 *ts, s32 *time_tai)
if (!(time_status & STA_NANO))
txc->time.tv_usec /= NSEC_PER_USEC;
+ /* Handle leapsec adjustments */
+ if (unlikely(ts->tv_sec >= ntp_next_leap_sec)) {
+ if ((time_state == TIME_INS) && (time_status & STA_INS)) {
+ result = TIME_OOP;
+ txc->tai++;
+ txc->time.tv_sec--;
+ }
+ if ((time_state == TIME_DEL) && (time_status & STA_DEL)) {
+ result = TIME_WAIT;
+ txc->tai--;
+ txc->time.tv_sec++;
+ }
+ if ((time_state == TIME_OOP) &&
+ (ts->tv_sec == ntp_next_leap_sec)) {
+ result = TIME_WAIT;
+ }
+ }
+
return result;
}