cpu/hotplug: Convert the hotplugged cpu work to a state machine

Move the functions which need to run on the hotplugged processor into
a state machine array and let the code iterate through these functions.

In a later state, this will grow synchronization points between the
control processor and the hotplugged processor, so we can move the
various architecture implementations of the synchronizations to the
core.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: Rik van Riel <riel@redhat.com>
Cc: Rafael Wysocki <rafael.j.wysocki@intel.com>
Cc: "Srivatsa S. Bhat" <srivatsa@mit.edu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Turner <pjt@google.com>
Link: http://lkml.kernel.org/r/20160226182340.770651526@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 70 insertions, 15 deletions

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index d55c9e64acd7..d9303cca83d3 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -6,6 +6,10 @@ enum cpuhp_state {
         CPUHP_CREATE_THREADS,
         CPUHP_NOTIFY_PREPARE,
         CPUHP_BRINGUP_CPU,
+        CPUHP_AP_OFFLINE,
+        CPUHP_AP_NOTIFY_STARTING,
+        CPUHP_AP_ONLINE,
+        CPUHP_TEARDOWN_CPU,
         CPUHP_NOTIFY_ONLINE,
         CPUHP_ONLINE,
 };
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 301851974b8d..797723e81756 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -57,6 +57,7 @@ struct cpuhp_step {
 };
 
 static struct cpuhp_step cpuhp_bp_states[];
+static struct cpuhp_step cpuhp_ap_states[];
 
 /**
  * cpuhp_invoke_callback _ Invoke the callbacks for a given state
@@ -304,6 +305,12 @@ static int notify_online(unsigned int cpu)
         return 0;
 }
 
+static int notify_starting(unsigned int cpu)
+{
+        cpu_notify(CPU_STARTING, cpu);
+        return 0;
+}
+
 static int bringup_cpu(unsigned int cpu)
 {
         struct task_struct *idle = idle_thread_get(cpu);
@@ -421,9 +428,17 @@ static int notify_down_prepare(unsigned int cpu)
         return err;
 }
 
+static int notify_dying(unsigned int cpu)
+{
+        cpu_notify(CPU_DYING, cpu);
+        return 0;
+}
+
 /* Take this CPU down. */
 static int take_cpu_down(void *_param)
 {
+        struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
+        enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
         int err, cpu = smp_processor_id();
 
         /* Ensure this CPU doesn't handle any more interrupts. */
@@ -431,7 +446,12 @@ static int take_cpu_down(void *_param)
         if (err < 0)
                 return err;
 
-        cpu_notify(CPU_DYING, cpu);
+        /* Invoke the former CPU_DYING callbacks */
+        for (; st->state > target; st->state--) {
+                struct cpuhp_step *step = cpuhp_ap_states + st->state;
+
+                cpuhp_invoke_callback(cpu, st->state, step->teardown);
+        }
         /* Give up timekeeping duties */
         tick_handover_do_timer();
         /* Park the stopper thread */
@@ -512,6 +532,7 @@ static int notify_dead(unsigned int cpu)
 #define notify_down_prepare     NULL
 #define takedown_cpu            NULL
 #define notify_dead             NULL
+#define notify_dying            NULL
 #endif
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -615,6 +636,28 @@ void smpboot_thread_init(void)
         register_cpu_notifier(&smpboot_thread_notifier);
 }
 
+/**
+ * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
+ * @cpu: cpu that just started
+ *
+ * This function calls the cpu_chain notifiers with CPU_STARTING.
+ * It must be called by the arch code on the new cpu, before the new cpu
+ * enables interrupts and before the "boot" cpu returns from __cpu_up().
+ */
+void notify_cpu_starting(unsigned int cpu)
+{
+        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
+        enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
+
+        while (st->state < target) {
+                struct cpuhp_step *step;
+
+                st->state++;
+                step = cpuhp_ap_states + st->state;
+                cpuhp_invoke_callback(cpu, st->state, step->startup);
+        }
+}
+
 static void undo_cpu_up(unsigned int cpu, struct cpuhp_cpu_state *st)
 {
         for (st->state--; st->state > st->target; st->state--) {
@@ -842,19 +885,6 @@ core_initcall(cpu_hotplug_pm_sync_init);
 
 #endif /* CONFIG_PM_SLEEP_SMP */
 
-/**
- * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
- * @cpu: cpu that just started
- *
- * This function calls the cpu_chain notifiers with CPU_STARTING.
- * It must be called by the arch code on the new cpu, before the new cpu
- * enables interrupts and before the "boot" cpu returns from __cpu_up().
- */
-void notify_cpu_starting(unsigned int cpu)
-{
-        cpu_notify(CPU_STARTING, cpu);
-}
-
 #endif /* CONFIG_SMP */
 
 /* Boot processor state steps */
@@ -879,8 +909,12 @@ static struct cpuhp_step cpuhp_bp_states[] = {
         [CPUHP_BRINGUP_CPU] = {
                 .name                   = "cpu:bringup",
                 .startup                = bringup_cpu,
+                .teardown               = NULL,
+        },
+        [CPUHP_TEARDOWN_CPU] = {
+                .name                   = "cpu:teardown",
+                .startup                = NULL,
                 .teardown               = takedown_cpu,
-                .skip_onerr             = true,
         },
         [CPUHP_NOTIFY_ONLINE] = {
                 .name                   = "notify:online",
@@ -895,6 +929,23 @@ static struct cpuhp_step cpuhp_bp_states[] = {
         },
 };
 
+/* Application processor state steps */
+static struct cpuhp_step cpuhp_ap_states[] = {
+#ifdef CONFIG_SMP
+        [CPUHP_AP_NOTIFY_STARTING] = {
+                .name                   = "notify:starting",
+                .startup                = notify_starting,
+                .teardown               = notify_dying,
+                .skip_onerr             = true,
+        },
+#endif
+        [CPUHP_ONLINE] = {
+                .name                   = "online",
+                .startup                = NULL,
+                .teardown               = NULL,
+        },
+};
+
 /*
  * cpu_bit_bitmap[] is a special, "compressed" data structure that
  * represents all NR_CPUS bits binary values of 1<<nr.