From: Thomas Gleixner <tglx@linutronix.de>

BugLink: http://bugs.launchpad.net/bugs/1020285

This is a backport of f6c06abfb3972ad4914cef57d8348fcb2932bc3b

To finally fix the infamous leap second issue and other race windows
caused by functions which change the offsets between the various time
bases (CLOCK_MONOTONIC, CLOCK_REALTIME and CLOCK_BOOTTIME) we need a
function which atomically gets the current monotonic time and updates
the offsets of CLOCK_REALTIME and CLOCK_BOOTTIME with minimalistic
overhead. The previous patch which provides ktime_t offsets allows us
to make this function almost as cheap as ktime_get() which is going to
be replaced in hrtimer_interrupt().

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Prarit Bhargava <prarit@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Link: http://lkml.kernel.org/r/1341960205-56738-7-git-send-email-johnstul@us.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
include/linux/hrtimer.h | 2 +-
kernel/time/timekeeping.c | 32 ++++++++++++++++++++++++++++++++
2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index a7f48af..b4f0b3f 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -319,7 +319,7 @@ static inline void clock_was_set_delayed(void) { }

extern ktime_t ktime_get(void);
extern ktime_t ktime_get_real(void);
-
+extern ktime_t ktime_get_update_offsets(ktime_t *offs_real);

DECLARE_PER_CPU(struct tick_device, tick_cpu_device);

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index c7fbc9f..6054b94 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -943,3 +943,35 @@ struct timespec get_monotonic_coarse(void)
now.tv_nsec + mono.tv_nsec);
return now;
}
+
+#ifdef CONFIG_HIGH_RES_TIMERS
+/**
+ * ktime_get_update_offsets - hrtimer helper
+ * @real: pointer to storage for monotonic -> realtime offset
+ *
+ * Returns current monotonic time and updates the offsets
+ * Called from hrtimer_interupt() or retrigger_next_event()
+ */
+ktime_t ktime_get_update_offsets(ktime_t *real)
+{
+ ktime_t now;
+ unsigned int seq;
+ u64 secs, nsecs;
+
+ do {
+ seq = read_seqbegin(&xtime_lock);
+
+ secs = xtime.tv_sec;
+ nsecs = xtime.tv_nsec;
+ nsecs += timekeeping_get_ns();
+ /* If arch requires, add in gettimeoffset() */
+ nsecs += arch_gettimeoffset();
+
+ *real = offs_real;
+ } while (read_seqretry(&xtime_lock, seq));
+
+ now = ktime_add_ns(ktime_set(secs, 0), nsecs);
+ now = ktime_sub(now, *real);
+ return now;
+}
+#endif
--
1.7.9.5


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