[PATCH] 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>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index 9a1d958..c36353e 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -237,6 +237,8 @@
*/
static inline void stop_hz_timer(void)
{
+ unsigned long flags;
+ unsigned long seq, next;
__u64 timer, todval;
if (sysctl_hz_timer != 0)
@@ -257,7 +259,11 @@
* 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)) {