linux-kernel - [097/104] rtc: Fix some bugs that allowed accumulating time drift in suspend/resume

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Message-Id: <20111207161222.762773568@clark.kroah.org>
Date:	Wed, 07 Dec 2011 08:12:39 -0800
From:	Greg KH <gregkh@...e.de>
To:	<linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
Cc:	<torvalds@...ux-foundation.org>, <akpm@...ux-foundation.org>,
	<alan@...rguk.ukuu.org.uk>,
	Arve Hjønnevåg <arve@...roid.com>,
	John Stultz <john.stultz@...aro.org>
Subject: [097/104] rtc: Fix some bugs that allowed accumulating time drift in suspend/resume

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

------------------

From: =?UTF-8?q?Arve=20Hj=C3=B8nnev=C3=A5g?= <arve@...roid.com>

commit 6a8943d9ec2567572fca25cf69ad45844d0141a3 upstream.

The current code checks if abs(delta_delta.tv_sec) is greater or
equal to two before it discards the old delta value, but this can
trigger at close to -1 seconds since -1.000000001 seconds is stored
as tv_sec -2 and tv_nsec 999999999 in a normalized timespec.

rtc_resume had an early return check if the rtc value had not changed
since rtc_suspend. This effectivly stops time for the duration of the
short sleep. Check if sleep_time is positive after all the adjustments
have been applied instead since this allows the old_system adjustment
in rtc_suspend to have an effect even for short sleep cycles.

Signed-off-by: Arve Hjønnevåg <arve@...roid.com>
Signed-off-by: John Stultz <john.stultz@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/rtc/class.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -66,7 +66,7 @@ static int rtc_suspend(struct device *de
 	 */
 	delta = timespec_sub(old_system, old_rtc);
 	delta_delta = timespec_sub(delta, old_delta);
-	if (abs(delta_delta.tv_sec)  >= 2) {
+	if (delta_delta.tv_sec < -2 || delta_delta.tv_sec >= 2) {
 		/*
 		 * if delta_delta is too large, assume time correction
 		 * has occured and set old_delta to the current delta.
@@ -100,9 +100,8 @@ static int rtc_resume(struct device *dev
 	rtc_tm_to_time(&tm, &new_rtc.tv_sec);
 	new_rtc.tv_nsec = 0;
 
-	if (new_rtc.tv_sec <= old_rtc.tv_sec) {
-		if (new_rtc.tv_sec < old_rtc.tv_sec)
-			pr_debug("%s:  time travel!\n", dev_name(&rtc->dev));
+	if (new_rtc.tv_sec < old_rtc.tv_sec) {
+		pr_debug("%s:  time travel!\n", dev_name(&rtc->dev));
 		return 0;
 	}
 
@@ -119,7 +118,8 @@ static int rtc_resume(struct device *dev
 	sleep_time = timespec_sub(sleep_time,
 			timespec_sub(new_system, old_system));
 
-	timekeeping_inject_sleeptime(&sleep_time);
+	if (sleep_time.tv_sec >= 0)
+		timekeeping_inject_sleeptime(&sleep_time);
 	return 0;
 }
 


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