Fix RTC updates from ntp (rhbz 985522)

kernel.spec

@@ -759,6 +759,9 @@ Patch25104: ansi_cprng-Fix-off-by-one-error-in-non-block-size-request.patch
 
 Patch25103: fix-arm-btrfs-build.patch
 
+#rhbz 985522
+Patch25107: ntp-Make-periodic-RTC-update-more-reliable.patch
+
 # END OF PATCH DEFINITIONS
 
 %endif
@@ -1478,6 +1481,9 @@ ApplyPatch fix-arm-btrfs-build.patch
 #CVE-2013-4345 rhbz 1007690 1009136
 ApplyPatch ansi_cprng-Fix-off-by-one-error-in-non-block-size-request.patch
 
+#rhbz 985522
+ApplyPatch ntp-Make-periodic-RTC-update-more-reliable.patch
+
 # END OF PATCH APPLICATIONS
 
 %endif
@@ -2282,6 +2288,9 @@ fi
 #                                    ||----w |
 #                                    ||     ||
 %changelog
+* Fri Sep 20 2013 Josh Boyer <jwboyer@fedoraproject.org>
+- Fix RTC updates from ntp (rhbz 985522)
+
 * Fri Sep 20 2013 Josh Boyer <jwboyer@fedoraproject.org> - 3.12.0-0.rc1.git4.1
 - Linux v3.12-rc1-250-g7b9e3a6
 

ntp-Make-periodic-RTC-update-more-reliable.patch

@@ -0,0 +1,44 @@
+From a97ad0c4b447a132a322cedc3a5f7fa4cab4b304 Mon Sep 17 00:00:00 2001
+From: Miroslav Lichvar <mlichvar@redhat.com>
+Date: Thu, 1 Aug 2013 19:31:35 +0200
+Subject: [PATCH] ntp: Make periodic RTC update more reliable
+
+The current code requires that the scheduled update of the RTC happens
+in the closest tick to the half of the second. This seems to be
+difficult to achieve reliably. The scheduled work may be missing the
+target time by a tick or two and be constantly rescheduled every second.
+
+Relax the limit to 10 ticks. As a typical RTC drifts in the 11-minute
+update interval by several milliseconds, this shouldn't affect the
+overall accuracy of the RTC much.
+
+Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
+Signed-off-by: John Stultz <john.stultz@linaro.org>
+---
+ kernel/time/ntp.c |    3 ++-
+ 1 file changed, 2 insertions(+), 1 deletion(-)
+
+diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
+index 8f5b3b9..ab1fa7c 100644
+--- a/kernel/time/ntp.c
++++ b/kernel/time/ntp.c
+@@ -475,6 +475,7 @@ static void sync_cmos_clock(struct work_struct *work)
+ 	 * called as close as possible to 500 ms before the new second starts.
+ 	 * This code is run on a timer.  If the clock is set, that timer
+ 	 * may not expire at the correct time.  Thus, we adjust...
++	 * We want the clock to be within a couple of ticks from the target.
+ 	 */
+ 	if (!ntp_synced()) {
+ 		/*
+@@ -485,7 +486,7 @@ static void sync_cmos_clock(struct work_struct *work)
+ 	}
+ 
+ 	getnstimeofday(&now);
+-	if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2) {
++	if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec * 5) {
+ 		struct timespec adjust = now;
+ 
+ 		fail = -ENODEV;
+-- 
+1.7.9.5
+