linux-kernel - [tip:timers/urgent] hrtimer: Fix incorrect tai offset calculation for non high-res timer systems

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Message-ID: <tip-2d926c15d629a13914ce3e5f26354f6a0ac99e70@git.kernel.org>
Date:	Wed, 4 Feb 2015 23:42:51 -0800
From:	tip-bot for John Stultz <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	mingo@...nel.org, hpa@...or.com, john.stultz@...aro.org,
	linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: [tip:timers/urgent] hrtimer:
  Fix incorrect tai offset calculation for non high-res timer systems

Commit-ID:  2d926c15d629a13914ce3e5f26354f6a0ac99e70
Gitweb:     http://git.kernel.org/tip/2d926c15d629a13914ce3e5f26354f6a0ac99e70
Author:     John Stultz <john.stultz@...aro.org>
AuthorDate: Wed, 4 Feb 2015 16:45:26 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 5 Feb 2015 08:39:37 +0100

hrtimer: Fix incorrect tai offset calculation for non high-res timer systems

I noticed some CLOCK_TAI timer test failures on one of my
less-frequently used configurations. And after digging in I
found in 76f4108892d9 (Cleanup hrtimer accessors to the
timekepeing state), the hrtimer_get_softirq_time tai offset
calucation was incorrectly rewritten, as the tai offset we
return shold be from CLOCK_MONOTONIC, and not CLOCK_REALTIME.

This results in CLOCK_TAI timers expiring early on non-highres
capable machines.

This patch fixes the issue, calculating the tai time properly
from the monotonic base.

Signed-off-by: John Stultz <john.stultz@...aro.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: stable <stable@...r.kernel.org> # 3.17+
Link: http://lkml.kernel.org/r/1423097126-10236-1-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/time/hrtimer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 37e50aa..d8c724c 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -122,7 +122,7 @@ static void hrtimer_get_softirq_time(struct hrtimer_cpu_base *base)
 	mono = ktime_get_update_offsets_tick(&off_real, &off_boot, &off_tai);
 	boot = ktime_add(mono, off_boot);
 	xtim = ktime_add(mono, off_real);
-	tai = ktime_add(xtim, off_tai);
+	tai = ktime_add(mono, off_tai);
 
 	base->clock_base[HRTIMER_BASE_REALTIME].softirq_time = xtim;
 	base->clock_base[HRTIMER_BASE_MONOTONIC].softirq_time = mono;
--
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