[patch 3/3] nohz/s390: fix arch_needs_cpu() return value on offline cpus

[Heiko Carstens <heiko.carstens@de.ibm.com>]

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From: Heiko Carstens <heiko.carstens@de.ibm.com>

This fixes the same problem as described in the patch "nohz: fix
printk_needs_cpu() return value on offline cpus" for the arch_needs_cpu()
primitive.
This specific bug was indrocuded with 3c5d92a0 "nohz: Introduce arch_needs_cpu".

In this case a cpu hotplug notifier is used to fix the issue in order to keep
the normal/fast path small. All we need to do is to clear the condition that
makes arch_needs_cpu() return 1 since it is just a performance improvement which
is supposed to keep the local tick running for a short period if a cpu goes
idle. Nothing special needs to be done except for clearing the condition.

Cc: stable@kernel.org
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
---
 arch/s390/kernel/vtime.c |   19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -19,6 +19,7 @@
 #include <linux/kernel_stat.h>
 #include <linux/rcupdate.h>
 #include <linux/posix-timers.h>
+#include <linux/cpu.h>
 
 #include <asm/s390_ext.h>
 #include <asm/timer.h>
@@ -566,6 +567,23 @@ void init_cpu_vtimer(void)
 	__ctl_set_bit(0,10);
 }
 
+static int __cpuinit s390_nohz_notify(struct notifier_block *self,
+				      unsigned long action, void *hcpu)
+{
+	struct s390_idle_data *idle;
+	long cpu = (long) hcpu;
+
+	idle = &per_cpu(s390_idle, cpu);
+	switch (action) {
+	case CPU_DYING:
+	case CPU_DYING_FROZEN:
+		idle->nohz_delay = 0;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}
+
 void __init vtime_init(void)
 {
 	/* request the cpu timer external interrupt */
@@ -574,5 +592,6 @@ void __init vtime_init(void)
 
 	/* Enable cpu timer interrupts on the boot cpu. */
 	init_cpu_vtimer();
+	cpu_notifier(s390_nohz_notify, 0);
 }