linux-kernel - [PATCH 5/9] timekeeping: Fix CLOCK

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Message-Id: <1388701407-5029-5-git-send-email-john.stultz@linaro.org>
Date:	Thu,  2 Jan 2014 14:23:23 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	John Stultz <john.stultz@...aro.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Prarit Bhargava <prarit@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	Ingo Molnar <mingo@...nel.org>, stable <stable@...r.kernel.org>
Subject: [PATCH 5/9] timekeeping: Fix CLOCK_TAI timer/nanosleep delays

A think-o in the calculation of the monotonic -> tai time offset
results in CLOCK_TAI timers and nanosleeps to expire late (the
latency is ~2x the tai offset).

Fix this by adding the tai offset from the realtime offset instead
of subtracting.

Cc: Sasha Levin <sasha.levin@...cle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Prarit Bhargava <prarit@...hat.com>
Cc: Richard Cochran <richardcochran@...il.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: stable <stable@...r.kernel.org> #3.10+
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
 kernel/time/timekeeping.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 44b7e6b..3f6a827 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -77,7 +77,7 @@ static void tk_set_wall_to_mono(struct timekeeper *tk, struct timespec wtm)
 	tk->wall_to_monotonic = wtm;
 	set_normalized_timespec(&tmp, -wtm.tv_sec, -wtm.tv_nsec);
 	tk->offs_real = timespec_to_ktime(tmp);
-	tk->offs_tai = ktime_sub(tk->offs_real, ktime_set(tk->tai_offset, 0));
+	tk->offs_tai = ktime_add(tk->offs_real, ktime_set(tk->tai_offset, 0));
 }
 
 static void tk_set_sleep_time(struct timekeeper *tk, struct timespec t)
@@ -595,7 +595,7 @@ s32 timekeeping_get_tai_offset(void)
 static void __timekeeping_set_tai_offset(struct timekeeper *tk, s32 tai_offset)
 {
 	tk->tai_offset = tai_offset;
-	tk->offs_tai = ktime_sub(tk->offs_real, ktime_set(tai_offset, 0));
+	tk->offs_tai = ktime_add(tk->offs_real, ktime_set(tai_offset, 0));
 }
 
 /**
-- 
1.8.3.2

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