timekeeping: Provide hrtimer update function

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>

1 files changed, 34 insertions, 0 deletions

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 1c038dac71a2..269b1fe5f2ae 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1271,6 +1271,40 @@ void get_xtime_and_monotonic_and_sleep_offset(struct timespec *xtim,
         } while (read_seqretry(&timekeeper.lock, seq));
 }
 
+#ifdef CONFIG_HIGH_RES_TIMERS
+/**
+ * ktime_get_update_offsets - hrtimer helper
+ * @offs_real:  pointer to storage for monotonic -> realtime offset
+ * @offs_boot:  pointer to storage for monotonic -> boottime 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 *offs_real, ktime_t *offs_boot)
+{
+        ktime_t now;
+        unsigned int seq;
+        u64 secs, nsecs;
+
+        do {
+                seq = read_seqbegin(&timekeeper.lock);
+
+                secs = timekeeper.xtime.tv_sec;
+                nsecs = timekeeper.xtime.tv_nsec;
+                nsecs += timekeeping_get_ns();
+                /* If arch requires, add in gettimeoffset() */
+                nsecs += arch_gettimeoffset();
+
+                *offs_real = timekeeper.offs_real;
+                *offs_boot = timekeeper.offs_boot;
+        } while (read_seqretry(&timekeeper.lock, seq));
+
+        now = ktime_add_ns(ktime_set(secs, 0), nsecs);
+        now = ktime_sub(now, *offs_real);
+        return now;
+}
+#endif
+
 /**
  * ktime_get_monotonic_offset() - get wall_to_monotonic in ktime_t format
  */