[PATCH] s390: idle timer setup

Fix overflow in calculation of the new tod value in stop_hz_timer and fix
wrong virtual timer list idle time in case the virtual timer is already
expired in stop_cpu_timer.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/s390/kernel/time.c

@@ -244,7 +244,7 @@ int sysctl_hz_timer = 1;
  */
 static inline void stop_hz_timer(void)
 {
-	__u64 timer;
+	__u64 timer, todval;
 
 	if (sysctl_hz_timer != 0)
 		return;
@@ -265,8 +265,14 @@ static inline void stop_hz_timer(void)
 	 * for the next event.
 	 */
 	timer = (__u64) (next_timer_interrupt() - jiffies) + jiffies_64;
-	timer = jiffies_timer_cc + timer * CLK_TICKS_PER_JIFFY;
-	asm volatile ("SCKC %0" : : "m" (timer));
+	todval = -1ULL;
+	/* Be careful about overflows. */
+	if (timer < (-1ULL / CLK_TICKS_PER_JIFFY)) {
+		timer = jiffies_timer_cc + timer * CLK_TICKS_PER_JIFFY;
+		if (timer >= jiffies_timer_cc)
+			todval = timer;
+	}
+	asm volatile ("SCKC %0" : : "m" (todval));
 }
 
 /*

arch/s390/kernel/vtime.c

@@ -122,12 +122,17 @@ static void start_cpu_timer(void)
 	struct vtimer_queue *vt_list;
 
 	vt_list = &per_cpu(virt_cpu_timer, smp_processor_id());
-	set_vtimer(vt_list->idle);
+
+	/* CPU timer interrupt is pending, don't reprogramm it */
+	if (vt_list->idle & 1LL<<63)
+		return;
+
+	if (!list_empty(&vt_list->list))
+		set_vtimer(vt_list->idle);
 }
 
 static void stop_cpu_timer(void)
 {
-	__u64 done;
 	struct vtimer_queue *vt_list;
 
 	vt_list = &per_cpu(virt_cpu_timer, smp_processor_id());
@@ -138,21 +143,17 @@ static void stop_cpu_timer(void)
 		goto fire;
 	}
 
-	/* store progress */
-	asm volatile ("STPT %0" : "=m" (done));
+	/* store the actual expire value */
+	asm volatile ("STPT %0" : "=m" (vt_list->idle));
 
 	/*
-	 * If done is negative we do not stop the CPU timer
-	 * because we will get instantly an interrupt that
-	 * will start the CPU timer again.
+	 * If the CPU timer is negative we don't reprogramm
+	 * it because we will get instantly an interrupt.
 	 */
-	if (done & 1LL<<63)
+	if (vt_list->idle & 1LL<<63)
 		return;
-	else
-		vt_list->offset += vt_list->to_expire - done;
 
-	/* save the actual expire value */
-	vt_list->idle = done;
+	vt_list->offset += vt_list->to_expire - vt_list->idle;
 
 	/*
 	 * We cannot halt the CPU timer, we just write a value that