[PATCH 3.18 37/39] hrtimer: Fix incorrect tai offset calculation for non high-res timer systems

From: Greg Kroah-Hartman
Date: Mon Feb 09 2015 - 03:44:35 EST

3.18-stable review patch. If anyone has any objections, please let me know.


From: John Stultz <john.stultz@xxxxxxxxxx>

commit 2d926c15d629a13914ce3e5f26354f6a0ac99e70 upstream.

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@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1423097126-10236-1-git-send-email-john.stultz@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

kernel/time/hrtimer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -122,7 +122,7 @@ static void hrtimer_get_softirq_time(str
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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