[patch 3/14] s390: stop_hz_timer vs. xtime updates.

[patch 3/14] s390: stop_hz_timer vs. xtime updates.

[Martin Schwidefsky]

From: Martin Schwidefsky <schwidefsky@de.ibm.com>

[patch 3/14] s390: stop_hz_timer vs. xtime updates.

The calculation of the value return by next_timer_interrupt from
jiffies to jiffies_64 is racy against xtime updates. We need to
protect the calculation with read_seqbegin/read_seqretry.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---

 arch/s390/kernel/time.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletion(-)

diff -urpN linux-2.6/arch/s390/kernel/time.c linux-2.6-patched/arch/s390/kernel/time.c
--- linux-2.6/arch/s390/kernel/time.c	2005-10-28 02:02:08.000000000 +0200
+++ linux-2.6-patched/arch/s390/kernel/time.c	2005-10-28 14:04:45.000000000 +0200
@@ -241,6 +241,8 @@ int sysctl_hz_timer = 1;
  */
 static inline void stop_hz_timer(void)
 {
+	unsigned long flags;
+	unsigned long seq, next;
 	__u64 timer, todval;
 
 	if (sysctl_hz_timer != 0)
@@ -261,7 +263,11 @@ static inline void stop_hz_timer(void)
 	 * This cpu is going really idle. Set up the clock comparator
 	 * for the next event.
 	 */
-	timer = (__u64) (next_timer_interrupt() - jiffies) + jiffies_64;
+	next = next_timer_interrupt();
+	do {
+		seq = read_seqbegin_irqsave(&xtime_lock, flags);
+		timer = (__u64)(next - jiffies) + jiffies_64;
+	} while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
 	todval = -1ULL;
 	/* Be careful about overflows. */
 	if (timer < (-1ULL / CLK_TICKS_PER_JIFFY)) {