[tip:smp/hotplug] sched/hotplug: Make activate() the last hotplug step

[tip-bot for Thomas Gleixner]

Commit-ID:  aaddd7d1c740ab3c5efaad7a34650b6dc680c21c
Gitweb:     http://git.kernel.org/tip/aaddd7d1c740ab3c5efaad7a34650b6dc680c21c
Author:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Thu, 10 Mar 2016 12:54:19 +0100
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 6 May 2016 14:58:25 +0200

sched/hotplug: Make activate() the last hotplug step

The scheduler can handle per cpu threads before the cpu is set to active and
it does not allow user space threads on the cpu before active is
set. Attaching to the scheduling domains is also not required before user
space threads can be handled.

Move the activation to the end of the hotplug state space. That also means
that deactivation is the first action when a cpu is shut down.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: rt@xxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20160310120025.597477199@xxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 include/linux/cpuhotplug.h |  2 +-
 kernel/cpu.c               | 15 +++++++++------
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 9e07468..386374d 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -13,11 +13,11 @@ enum cpuhp_state {
 	CPUHP_AP_ONLINE,
 	CPUHP_TEARDOWN_CPU,
 	CPUHP_AP_ONLINE_IDLE,
-	CPUHP_AP_ACTIVE,
 	CPUHP_AP_SMPBOOT_THREADS,
 	CPUHP_AP_NOTIFY_ONLINE,
 	CPUHP_AP_ONLINE_DYN,
 	CPUHP_AP_ONLINE_DYN_END		= CPUHP_AP_ONLINE_DYN + 30,
+	CPUHP_AP_ACTIVE,
 	CPUHP_ONLINE,
 };
 
diff --git a/kernel/cpu.c b/kernel/cpu.c
index d6eeb8c..d948e44 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1242,12 +1242,6 @@ static struct cpuhp_step cpuhp_ap_states[] = {
 	[CPUHP_AP_ONLINE] = {
 		.name			= "ap:online",
 	},
-	/* First state is scheduler control. Interrupts are enabled */
-	[CPUHP_AP_ACTIVE] = {
-		.name			= "sched:active",
-		.startup		= sched_cpu_activate,
-		.teardown		= sched_cpu_deactivate,
-	},
 	/* Handle smpboot threads park/unpark */
 	[CPUHP_AP_SMPBOOT_THREADS] = {
 		.name			= "smpboot:threads",
@@ -1269,6 +1263,15 @@ static struct cpuhp_step cpuhp_ap_states[] = {
 	 * The dynamically registered state space is here
 	 */
 
+#ifdef CONFIG_SMP
+	/* Last state is scheduler control setting the cpu active */
+	[CPUHP_AP_ACTIVE] = {
+		.name			= "sched:active",
+		.startup		= sched_cpu_activate,
+		.teardown		= sched_cpu_deactivate,
+	},
+#endif
+
 	/* CPU is fully up and running. */
 	[CPUHP_ONLINE] = {
 		.name			= "online",