linux-kernel - [PATCH 10/11] ntp: Fix second_overflow's input parameter type to be 64bits

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Date:	Fri, 18 Dec 2015 13:39:15 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	DengChao <chao.deng@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Miroslav Lichvar <mlichvar@...hat.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	John Stultz <john.stultz@...aro.org>
Subject: [PATCH 10/11] ntp: Fix second_overflow's input parameter type to be 64bits

From: DengChao <chao.deng@...aro.org>

The function "second_overflow" uses "unsign long"
as its input parameter type which will overflow after
year 2106 on 32bit systems.

Thus this patch replaces it with time64_t type.

While the 64-bit division is expensive, "next_ntp_leap_sec"
has been calculated already, so we can just re-use it in the
TIME_INS/DEL cases, allowing one expensive division per
leapsecond instead of re-doing the divsion once a second after
the leap flag has been set.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Miroslav Lichvar <mlichvar@...hat.com>
Cc: Prarit Bhargava <prarit@...hat.com>
Cc: Richard Cochran <richardcochran@...il.com>
Signed-off-by: DengChao <chao.deng@...aro.org>
[jstultz: Tweaked commit message]
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
 kernel/time/ntp.c          | 16 +++++++++-------
 kernel/time/ntp_internal.h |  2 +-
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index e947bfd..36f2ca0 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -16,6 +16,7 @@
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/rtc.h>
+#include <linux/math64.h>
 
 #include "ntp_internal.h"
 #include "timekeeping_internal.h"
@@ -394,10 +395,11 @@ ktime_t ntp_get_next_leap(void)
  *
  * Also handles leap second processing, and returns leap offset
  */
-int second_overflow(unsigned long secs)
+int second_overflow(time64_t secs)
 {
 	s64 delta;
 	int leap = 0;
+	s32 rem;
 
 	/*
 	 * Leap second processing. If in leap-insert state at the end of the
@@ -408,19 +410,19 @@ int second_overflow(unsigned long secs)
 	case TIME_OK:
 		if (time_status & STA_INS) {
 			time_state = TIME_INS;
-			ntp_next_leap_sec = secs + SECS_PER_DAY -
-						(secs % SECS_PER_DAY);
+			div_s64_rem(secs, SECS_PER_DAY, &rem);
+			ntp_next_leap_sec = secs + SECS_PER_DAY - rem;
 		} else if (time_status & STA_DEL) {
 			time_state = TIME_DEL;
-			ntp_next_leap_sec = secs + SECS_PER_DAY -
-						 ((secs+1) % SECS_PER_DAY);
+			div_s64_rem(secs + 1, SECS_PER_DAY, &rem);
+			ntp_next_leap_sec = secs + SECS_PER_DAY - rem;
 		}
 		break;
 	case TIME_INS:
 		if (!(time_status & STA_INS)) {
 			ntp_next_leap_sec = TIME64_MAX;
 			time_state = TIME_OK;
-		} else if (secs % SECS_PER_DAY == 0) {
+		} else if (secs == ntp_next_leap_sec) {
 			leap = -1;
 			time_state = TIME_OOP;
 			printk(KERN_NOTICE
@@ -431,7 +433,7 @@ int second_overflow(unsigned long secs)
 		if (!(time_status & STA_DEL)) {
 			ntp_next_leap_sec = TIME64_MAX;
 			time_state = TIME_OK;
-		} else if ((secs + 1) % SECS_PER_DAY == 0) {
+		} else if (secs == ntp_next_leap_sec) {
 			leap = 1;
 			ntp_next_leap_sec = TIME64_MAX;
 			time_state = TIME_WAIT;
diff --git a/kernel/time/ntp_internal.h b/kernel/time/ntp_internal.h
index af92447..d8a7c11 100644
--- a/kernel/time/ntp_internal.h
+++ b/kernel/time/ntp_internal.h
@@ -6,7 +6,7 @@ extern void ntp_clear(void);
 /* Returns how long ticks are at present, in ns / 2^NTP_SCALE_SHIFT. */
 extern u64 ntp_tick_length(void);
 extern ktime_t ntp_get_next_leap(void);
-extern int second_overflow(unsigned long secs);
+extern int second_overflow(time64_t secs);
 extern int ntp_validate_timex(struct timex *);
 extern int __do_adjtimex(struct timex *, struct timespec64 *, s32 *);
 extern void __hardpps(const struct timespec64 *, const struct timespec64 *);
-- 
1.9.1

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