[patch 07/40] cpu: hotplug: Convert to a state machine for the control processor

[Thomas Gleixner <tglx@linutronix.de>]

[-- Attachment #1: cpu-hotplug-implement-state-machine.patch --]
[-- Type: text/plain, Size: 10292 bytes --]

Move the split out steps into a callback array and let the cpu_up/down
code iterate through the array functions. For now most of the
callbacks are asymetric to resemble the current hotplug maze.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/cpu.h        |    4 +
 include/linux/cpuhotplug.h |   16 ++++
 init/main.c                |   15 ---
 kernel/cpu.c               |  180 ++++++++++++++++++++++++++++++++++++---------
 kernel/smpboot.c           |    6 +
 kernel/smpboot.h           |    4 -
 6 files changed, 173 insertions(+), 52 deletions(-)

Index: linux-2.6/include/linux/cpu.h
===================================================================
--- linux-2.6.orig/include/linux/cpu.h
+++ linux-2.6/include/linux/cpu.h
@@ -26,6 +26,9 @@ struct cpu {
 	struct device dev;
 };
 
+extern void boot_cpu_init(void);
+extern void boot_cpu_state_init(void);
+
 extern int register_cpu(struct cpu *cpu, int num);
 extern struct device *get_cpu_device(unsigned cpu);
 extern bool cpu_is_hotpluggable(unsigned cpu);
@@ -112,6 +115,7 @@ enum {
 
 
 #ifdef CONFIG_SMP
+extern bool cpuhp_tasks_frozen;
 /* Need to know about CPUs going up/down? */
 #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE)
 #define cpu_notifier(fn, pri) {					\
Index: linux-2.6/include/linux/cpuhotplug.h
===================================================================
--- /dev/null
+++ linux-2.6/include/linux/cpuhotplug.h
@@ -0,0 +1,16 @@
+#ifndef __CPUHOTPLUG_H
+#define __CPUHOTPLUG_H
+
+enum cpuhp_states {
+	CPUHP_OFFLINE,
+	CPUHP_CREATE_THREADS,
+	CPUHP_NOTIFY_PREPARE,
+	CPUHP_NOTIFY_DEAD,
+	CPUHP_BRINGUP_CPU,
+	CPUHP_TEARDOWN_CPU,
+	CPUHP_PERCPU_THREADS,
+	CPUHP_NOTIFY_ONLINE,
+	CPUHP_NOTIFY_DOWN_PREPARE,
+	CPUHP_MAX,
+};
+#endif
Index: linux-2.6/init/main.c
===================================================================
--- linux-2.6.orig/init/main.c
+++ linux-2.6/init/main.c
@@ -424,20 +424,6 @@ void __init parse_early_param(void)
 	done = 1;
 }
 
-/*
- *	Activate the first processor.
- */
-
-static void __init boot_cpu_init(void)
-{
-	int cpu = smp_processor_id();
-	/* Mark the boot cpu "present", "online" etc for SMP and UP case */
-	set_cpu_online(cpu, true);
-	set_cpu_active(cpu, true);
-	set_cpu_present(cpu, true);
-	set_cpu_possible(cpu, true);
-}
-
 void __init __weak smp_setup_processor_id(void)
 {
 }
@@ -502,6 +488,7 @@ asmlinkage void __init start_kernel(void
 	setup_command_line(command_line);
 	setup_nr_cpu_ids();
 	setup_per_cpu_areas();
+	boot_cpu_state_init();
 	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
 
 	build_all_zonelists(NULL, NULL);
Index: linux-2.6/kernel/cpu.c
===================================================================
--- linux-2.6.orig/kernel/cpu.c
+++ linux-2.6/kernel/cpu.c
@@ -19,13 +19,24 @@
 #include <linux/mutex.h>
 #include <linux/gfp.h>
 #include <linux/suspend.h>
+#include <linux/cpuhotplug.h>
 
 #include "smpboot.h"
 
+/* CPU state */
+static DEFINE_PER_CPU(enum cpuhp_states, cpuhp_state);
+
+struct cpuhp_step {
+	int (*startup)(unsigned int cpu);
+	int (*teardown)(unsigned int cpu);
+};
+
+static struct cpuhp_step cpuhp_bp_states[];
+
 #ifdef CONFIG_SMP
 /* Serializes the updates to cpu_online_mask, cpu_present_mask */
 static DEFINE_MUTEX(cpu_add_remove_lock);
-static bool cpuhp_tasks_frozen;
+bool cpuhp_tasks_frozen;
 
 /*
  * The following two API's must be used when attempting
@@ -310,13 +321,10 @@ static int __ref take_cpu_down(void *_pa
 
 static int takedown_cpu(unsigned int cpu)
 {
-	int err;
+	int err = __stop_machine(take_cpu_down, NULL, cpumask_of(cpu));
 
-	smpboot_park_threads(cpu);
-	err = __stop_machine(take_cpu_down, NULL, cpumask_of(cpu));
 	if (err) {
 		/* CPU didn't die: tell everyone.  Can't complain. */
-		smpboot_unpark_threads(cpu);
 		cpu_notify_nofail(CPU_DOWN_FAILED, cpu);
 		return err;
 	}
@@ -345,10 +353,32 @@ static int notify_dead(unsigned int cpu)
 	return 0;
 }
 
+#else
+#define notify_down_prepare	NULL
+#define takedown_cpu		NULL
+#define notify_dead		NULL
+#endif
+
+#ifdef CONFIG_HOTPLUG_CPU
+static void undo_cpu_down(unsigned int cpu, int step)
+{
+	while (step++ < CPUHP_MAX) {
+		/*
+		 * Transitional check. Will be removed when we have a
+		 * fully symetric mechanism
+		 */
+		if (!cpuhp_bp_states[step].teardown)
+			continue;
+
+		if (cpuhp_bp_states[step].startup)
+			cpuhp_bp_states[step].startup(cpu);
+	}
+}
+
 /* Requires cpu_add_remove_lock to be held */
 static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
 {
-	int err;
+	int ret = 0, step;
 
 	if (num_online_cpus() == 1)
 		return -EBUSY;
@@ -360,20 +390,23 @@ static int __ref _cpu_down(unsigned int 
 
 	cpuhp_tasks_frozen = tasks_frozen;
 
-	err = notify_down_prepare(cpu);
-	if (err)
-		goto out_release;
-	err = takedown_cpu(cpu);
-	if (err)
-		goto out_release;
-
-	notify_dead(cpu);
+	for (step = per_cpu(cpuhp_state, cpu); step > 0; step--) {
+		if (cpuhp_bp_states[step].teardown) {
+			ret = cpuhp_bp_states[step].teardown(cpu);
+			if (ret) {
+				undo_cpu_down(cpu, step + 1);
+				step = CPUHP_MAX;
+				break;
+			}
+		}
+	}
+	/* Store the current cpu state */
+	per_cpu(cpuhp_state, cpu) = step;
 
-out_release:
 	cpu_hotplug_done();
-	if (!err)
+	if (!ret)
 		cpu_notify_nofail(CPU_POST_DEAD, cpu);
-	return err;
+	return ret;
 }
 
 int __ref cpu_down(unsigned int cpu)
@@ -396,11 +429,25 @@ out:
 EXPORT_SYMBOL(cpu_down);
 #endif /*CONFIG_HOTPLUG_CPU*/
 
+static void undo_cpu_up(unsigned int cpu, int step)
+{
+	while (step--) {
+		/*
+		 * Transitional check. Will be removed when we have a
+		 * fully symetric mechanism
+		 */
+		if (!cpuhp_bp_states[step].startup)
+			continue;
+		if (cpuhp_bp_states[step].teardown)
+			cpuhp_bp_states[step].teardown(cpu);
+	}
+}
+
 /* Requires cpu_add_remove_lock to be held */
 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
 {
+	int ret = 0, step;
 	struct task_struct *idle;
-	int ret;
 
 	cpu_hotplug_begin();
 
@@ -409,6 +456,7 @@ static int __cpuinit _cpu_up(unsigned in
 		goto out;
 	}
 
+	/* Let it fail before we try to bring the cpu up */
 	idle = idle_thread_get(cpu);
 	if (IS_ERR(idle)) {
 		ret = PTR_ERR(idle);
@@ -417,24 +465,20 @@ static int __cpuinit _cpu_up(unsigned in
 
 	cpuhp_tasks_frozen = tasks_frozen;
 
-	ret = smpboot_create_threads(cpu);
-	if (ret)
-		goto out;
-
-	ret = notify_prepare(cpu);
-	if (ret)
-		goto out;
-
-	ret = bringup_cpu(cpu);
-	if (ret)
-		goto out;
-
-	/* Wake the per cpu threads */
-	smpboot_unpark_threads(cpu);
-	notify_online(cpu);
+	for (step = per_cpu(cpuhp_state, cpu); step < CPUHP_MAX; step++) {
+		if (cpuhp_bp_states[step].startup) {
+			ret = cpuhp_bp_states[step].startup(cpu);
+			if (ret) {
+				undo_cpu_up(cpu, step - 1);
+				step = 0;
+				break;
+			}
+		}
+	}
+	/* Store the current cpu state */
+	per_cpu(cpuhp_state, cpu) = step;
 out:
 	cpu_hotplug_done();
-
 	return ret;
 }
 
@@ -674,6 +718,52 @@ void __cpuinit notify_cpu_starting(unsig
 
 #endif /* CONFIG_SMP */
 
+/* Boot processor state steps */
+static struct cpuhp_step cpuhp_bp_states[] = {
+	[CPUHP_OFFLINE] = {
+		.startup = NULL,
+		.teardown = NULL,
+	},
+#ifdef CONFIG_SMP
+	[CPUHP_CREATE_THREADS] = {
+		.startup = smpboot_create_threads,
+		.teardown = NULL,
+	},
+	[CPUHP_NOTIFY_PREPARE] = {
+		.startup = notify_prepare,
+		.teardown = NULL,
+	},
+	[CPUHP_NOTIFY_DEAD] = {
+		.startup = NULL,
+		.teardown = notify_dead,
+	},
+	[CPUHP_BRINGUP_CPU] = {
+		.startup = bringup_cpu,
+		.teardown = NULL,
+	},
+	[CPUHP_TEARDOWN_CPU] = {
+		.startup = NULL,
+		.teardown = takedown_cpu,
+	},
+	[CPUHP_PERCPU_THREADS] = {
+		.startup = smpboot_unpark_threads,
+		.teardown = smpboot_park_threads,
+	},
+	[CPUHP_NOTIFY_ONLINE] = {
+		.startup = notify_online,
+		.teardown = NULL,
+	},
+	[CPUHP_NOTIFY_DOWN_PREPARE] = {
+		.startup = NULL,
+		.teardown = notify_down_prepare,
+	},
+#endif
+	[CPUHP_MAX] = {
+		.startup = NULL,
+		.teardown = NULL,
+	},
+};
+
 /*
  * cpu_bit_bitmap[] is a special, "compressed" data structure that
  * represents all NR_CPUS bits binary values of 1<<nr.
@@ -769,3 +859,25 @@ void init_cpu_online(const struct cpumas
 {
 	cpumask_copy(to_cpumask(cpu_online_bits), src);
 }
+
+/*
+ * Activate the first processor.
+ */
+void __init boot_cpu_init(void)
+{
+	int cpu = smp_processor_id();
+
+	/* Mark the boot cpu "present", "online" etc for SMP and UP case */
+	set_cpu_online(cpu, true);
+	set_cpu_active(cpu, true);
+	set_cpu_present(cpu, true);
+	set_cpu_possible(cpu, true);
+}
+
+/*
+ * Must be called _AFTER_ setting up the per_cpu areas
+ */
+void __init boot_cpu_state_init(void)
+{
+	per_cpu(cpuhp_state, smp_processor_id()) = CPUHP_MAX;
+}
Index: linux-2.6/kernel/smpboot.c
===================================================================
--- linux-2.6.orig/kernel/smpboot.c
+++ linux-2.6/kernel/smpboot.c
@@ -212,7 +212,7 @@ static void smpboot_unpark_thread(struct
 	kthread_unpark(tsk);
 }
 
-void smpboot_unpark_threads(unsigned int cpu)
+int smpboot_unpark_threads(unsigned int cpu)
 {
 	struct smp_hotplug_thread *cur;
 
@@ -220,6 +220,7 @@ void smpboot_unpark_threads(unsigned int
 	list_for_each_entry(cur, &hotplug_threads, list)
 		smpboot_unpark_thread(cur, cpu);
 	mutex_unlock(&smpboot_threads_lock);
+	return 0;
 }
 
 static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
@@ -230,7 +231,7 @@ static void smpboot_park_thread(struct s
 		kthread_park(tsk);
 }
 
-void smpboot_park_threads(unsigned int cpu)
+int smpboot_park_threads(unsigned int cpu)
 {
 	struct smp_hotplug_thread *cur;
 
@@ -238,6 +239,7 @@ void smpboot_park_threads(unsigned int c
 	list_for_each_entry_reverse(cur, &hotplug_threads, list)
 		smpboot_park_thread(cur, cpu);
 	mutex_unlock(&smpboot_threads_lock);
+	return 0;
 }
 
 static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
Index: linux-2.6/kernel/smpboot.h
===================================================================
--- linux-2.6.orig/kernel/smpboot.h
+++ linux-2.6/kernel/smpboot.h
@@ -14,7 +14,7 @@ static inline void idle_threads_init(voi
 #endif
 
 int smpboot_create_threads(unsigned int cpu);
-void smpboot_park_threads(unsigned int cpu);
-void smpboot_unpark_threads(unsigned int cpu);
+int smpboot_park_threads(unsigned int cpu);
+int smpboot_unpark_threads(unsigned int cpu);
 
 #endif