This is a note to let you know that I've just added the patch titled
timekeeping: Correct run-time detection of persistent_clock.
to the 3.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
timekeeping-correct-run-time-detection-of-persistent_clock.patch
and it can be found in the queue-3.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 0d6bd9953f739dad96d9a0de65383e479ab4e10d Mon Sep 17 00:00:00 2001
From: Zoran Markovic <zoran.markovic@xxxxxxxxxx>
Date: Fri, 17 May 2013 11:24:05 -0700
Subject: timekeeping: Correct run-time detection of persistent_clock.
From: Zoran Markovic <zoran.markovic@xxxxxxxxxx>
commit 0d6bd9953f739dad96d9a0de65383e479ab4e10d upstream.
Since commit 31ade30692dc9680bfc95700d794818fa3f754ac, timekeeping_init()
checks for presence of persistent clock by attempting to read a non-zero
time value. This is an issue on platforms where persistent_clock (instead
is implemented as a free-running counter (instead of an RTC) starting
from zero on each boot and running during suspend. Examples are some ARM
platforms (e.g. PandaBoard).
An attempt to read such a clock during timekeeping_init() may return zero
value and falsely declare persistent clock as missing. Additionally, in
the above case suspend times may be accounted twice (once from
timekeeping_resume() and once from rtc_resume()), resulting in a gradual
drift of system time.
This patch does a run-time correction of the issue by doing the same check
during timekeeping_suspend().
A better long-term solution would have to return error when trying to read
non-existing clock and zero when trying to read an uninitialized clock, but
that would require changing all persistent_clock implementations.
This patch addresses the immediate breakage, for now.
Signed-off-by: Zoran Markovic <zoran.markovic@xxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Feng Tang <feng.tang@xxxxxxxxx>
[jstultz: Tweaked commit message and subject]
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
[zoran.markovic@xxxxxxxxxx: reworked patch to fit 3.9-stable.]
Signed-off-by: Zoran Markovic <zoran.markovic@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/time/timekeeping.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -826,6 +826,14 @@ static int timekeeping_suspend(void)
read_persistent_clock(&timekeeping_suspend_time);
+ /*
+ * On some systems the persistent_clock can not be detected at
+ * timekeeping_init by its return value, so if we see a valid
+ * value returned, update the persistent_clock_exists flag.
+ */
+ if (timekeeping_suspend_time.tv_sec || timekeeping_suspend_time.tv_nsec)
+ persistent_clock_exist = true;
+
write_seqlock_irqsave(&tk->lock, flags);
timekeeping_forward_now(tk);
timekeeping_suspended = 1;
Patches currently in stable-queue which might be from zoran.markovic@xxxxxxxxxx are
queue-3.9/timekeeping-correct-run-time-detection-of-persistent_clock.patch
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