[S390] idle time accounting vs. machine checks

A machine check can interrupt the i/o and external interrupt handler
anytime. If the machine check occurs while the interrupt handler is
waking up from idle vtime_start_cpu can get executed a second time
and the int_clock / async_enter_timer values in the lowcore get
clobbered. This can confuse the cpu time accounting.
To fix this problem two changes are needed. First the machine check
handler has to use its own copies of int_clock and async_enter_timer,
named mcck_clock and mcck_enter_timer. Second the nested execution
of vtime_start_cpu has to be prevented. This is done in s390_idle_check
by checking the wait bit in the program status word.

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

1 files changed, 9 insertions, 6 deletions

diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c
index b59a812a010e..3479f1b0d4e0 100644
--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -121,32 +121,35 @@ void account_system_vtime(struct task_struct *tsk)
 }
 EXPORT_SYMBOL_GPL(account_system_vtime);
 
-void vtime_start_cpu(void)
+void vtime_start_cpu(__u64 int_clock, __u64 enter_timer)
 {
         struct s390_idle_data *idle = &__get_cpu_var(s390_idle);
         struct vtimer_queue *vq = &__get_cpu_var(virt_cpu_timer);
         __u64 idle_time, expires;
 
+        if (idle->idle_enter == 0ULL)
+                return;
+
         /* Account time spent with enabled wait psw loaded as idle time. */
-        idle_time = S390_lowcore.int_clock - idle->idle_enter;
+        idle_time = int_clock - idle->idle_enter;
         account_idle_time(idle_time);
         S390_lowcore.steal_timer +=
                 idle->idle_enter - S390_lowcore.last_update_clock;
-        S390_lowcore.last_update_clock = S390_lowcore.int_clock;
+        S390_lowcore.last_update_clock = int_clock;
 
         /* Account system time spent going idle. */
         S390_lowcore.system_timer += S390_lowcore.last_update_timer - vq->idle;
-        S390_lowcore.last_update_timer = S390_lowcore.async_enter_timer;
+        S390_lowcore.last_update_timer = enter_timer;
 
         /* Restart vtime CPU timer */
         if (vq->do_spt) {
                 /* Program old expire value but first save progress. */
-                expires = vq->idle - S390_lowcore.async_enter_timer;
+                expires = vq->idle - enter_timer;
                 expires += get_vtimer();
                 set_vtimer(expires);
         } else {
                 /* Don't account the CPU timer delta while the cpu was idle. */
-                vq->elapsed -= vq->idle - S390_lowcore.async_enter_timer;
+                vq->elapsed -= vq->idle - enter_timer;
         }
 
         idle->sequence++;