[RFC][PATCH -mm 2/2] x86_64: Detect clock skew during suspend

["Rafael J. Wysocki" <rjw@sisk.pl>]

Detect the situations in which the time after a resume from disk would
be earlier than the time before the suspend and prevent them from
happening on x86_64.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
 arch/x86_64/kernel/time.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletion(-)

Index: linux-2.6.18-rc4-mm1/arch/x86_64/kernel/time.c
===================================================================
--- linux-2.6.18-rc4-mm1.orig/arch/x86_64/kernel/time.c
+++ linux-2.6.18-rc4-mm1/arch/x86_64/kernel/time.c
@@ -1039,8 +1039,16 @@ static int timer_resume(struct sys_devic
 	unsigned long flags;
 	unsigned long sec;
 	unsigned long ctime = get_cmos_time();
-	unsigned long sleep_length = (ctime - sleep_start) * HZ;
+	long sleep_length = (ctime - sleep_start) * HZ;
 
+	if (sleep_length < 0) {
+		printk(KERN_WARNING "Time skew detected in timer resume!\n");
+		/* The time after the resume must not be earlier than the time
+		 * before the suspend or some nasty things will happen
+		 */
+		sleep_length = 0;
+		ctime = sleep_start;
+	}
 	if (vxtime.hpet_address)
 		hpet_reenable();
 	else