Merge branch 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull preparatory smp/hotplug patches from Ingo Molnar:
 "Some early preparatory changes for the WIP hotplug rework by Thomas
  Gleixner."

* 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  stop_machine: Use smpboot threads
  stop_machine: Store task reference in a separate per cpu variable
  smpboot: Allow selfparking per cpu threads

4 files changed, 70 insertions, 98 deletions

diff --git a/include/linux/smpboot.h b/include/linux/smpboot.h
index e0106d8581d3..c65dee059913 100644
--- a/include/linux/smpboot.h
+++ b/include/linux/smpboot.h
@@ -14,6 +14,8 @@ struct smpboot_thread_data;
  * @thread_should_run:  Check whether the thread should run or not. Called with
  *                      preemption disabled.
  * @thread_fn:          The associated thread function
+ * @create:             Optional setup function, called when the thread gets
+ *                      created (Not called from the thread context)
  * @setup:              Optional setup function, called when the thread gets
  *                      operational the first time
  * @cleanup:            Optional cleanup function, called when the thread
@@ -22,6 +24,7 @@ struct smpboot_thread_data;
  *                      parked (cpu offline)
  * @unpark:             Optional unpark function, called when the thread is
  *                      unparked (cpu online)
+ * @selfparking:        Thread is not parked by the park function.
  * @thread_comm:        The base name of the thread
  */
 struct smp_hotplug_thread {
@@ -29,10 +32,12 @@ struct smp_hotplug_thread {
         struct list_head                list;
         int                             (*thread_should_run)(unsigned int cpu);
         void                            (*thread_fn)(unsigned int cpu);
+        void                            (*create)(unsigned int cpu);
         void                            (*setup)(unsigned int cpu);
         void                            (*cleanup)(unsigned int cpu, bool online);
         void                            (*park)(unsigned int cpu);
         void                            (*unpark)(unsigned int cpu);
+        bool                            selfparking;
         const char                      *thread_comm;
 };
 
diff --git a/kernel/cpu.c b/kernel/cpu.c
index e5d5e8e1e030..b5e4ab2d427e 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -256,6 +256,8 @@ static int __ref take_cpu_down(void *_param)
                 return err;
 
         cpu_notify(CPU_DYING | param->mod, param->hcpu);
+        /* Park the stopper thread */
+        kthread_park(current);
         return 0;
 }
 
diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index d6c5fc054242..d4abac261779 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -183,9 +183,10 @@ __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
                 kfree(td);
                 return PTR_ERR(tsk);
         }
-
         get_task_struct(tsk);
         *per_cpu_ptr(ht->store, cpu) = tsk;
+        if (ht->create)
+                ht->create(cpu);
         return 0;
 }
 
@@ -225,7 +226,7 @@ static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
 {
         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 
-        if (tsk)
+        if (tsk && !ht->selfparking)
                 kthread_park(tsk);
 }
 
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 2f194e965715..95d178c62d5a 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -18,7 +18,7 @@
 #include <linux/stop_machine.h>
 #include <linux/interrupt.h>
 #include <linux/kallsyms.h>
-
+#include <linux/smpboot.h>
 #include <linux/atomic.h>
 
 /*
@@ -37,10 +37,10 @@ struct cpu_stopper {
         spinlock_t              lock;
         bool                    enabled;        /* is this stopper enabled? */
         struct list_head        works;          /* list of pending works */
-        struct task_struct      *thread;        /* stopper thread */
 };
 
 static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
+static DEFINE_PER_CPU(struct task_struct *, cpu_stopper_task);
 static bool stop_machine_initialized = false;
 
 static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
@@ -62,16 +62,18 @@ static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
 }
 
 /* queue @work to @stopper.  if offline, @work is completed immediately */
-static void cpu_stop_queue_work(struct cpu_stopper *stopper,
-                                struct cpu_stop_work *work)
+static void cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
 {
+        struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
+        struct task_struct *p = per_cpu(cpu_stopper_task, cpu);
+
         unsigned long flags;
 
         spin_lock_irqsave(&stopper->lock, flags);
 
         if (stopper->enabled) {
                 list_add_tail(&work->list, &stopper->works);
-                wake_up_process(stopper->thread);
+                wake_up_process(p);
         } else
                 cpu_stop_signal_done(work->done, false);
 
@@ -108,7 +110,7 @@ int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
         struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
 
         cpu_stop_init_done(&done, 1);
-        cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), &work);
+        cpu_stop_queue_work(cpu, &work);
         wait_for_completion(&done.completion);
         return done.executed ? done.ret : -ENOENT;
 }
@@ -130,7 +132,7 @@ void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
                         struct cpu_stop_work *work_buf)
 {
         *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
-        cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), work_buf);
+        cpu_stop_queue_work(cpu, work_buf);
 }
 
 /* static data for stop_cpus */
@@ -159,8 +161,7 @@ static void queue_stop_cpus_work(const struct cpumask *cpumask,
          */
         preempt_disable();
         for_each_cpu(cpu, cpumask)
-                cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu),
-                                    &per_cpu(stop_cpus_work, cpu));
+                cpu_stop_queue_work(cpu, &per_cpu(stop_cpus_work, cpu));
         preempt_enable();
 }
 
@@ -244,20 +245,25 @@ int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
         return ret;
 }
 
-static int cpu_stopper_thread(void *data)
+static int cpu_stop_should_run(unsigned int cpu)
+{
+        struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
+        unsigned long flags;
+        int run;
+
+        spin_lock_irqsave(&stopper->lock, flags);
+        run = !list_empty(&stopper->works);
+        spin_unlock_irqrestore(&stopper->lock, flags);
+        return run;
+}
+
+static void cpu_stopper_thread(unsigned int cpu)
 {
-        struct cpu_stopper *stopper = data;
+        struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
         struct cpu_stop_work *work;
         int ret;
 
 repeat:
-        set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
-
-        if (kthread_should_stop()) {
-                __set_current_state(TASK_RUNNING);
-                return 0;
-        }
-
         work = NULL;
         spin_lock_irq(&stopper->lock);
         if (!list_empty(&stopper->works)) {
@@ -273,8 +279,6 @@ repeat:
                 struct cpu_stop_done *done = work->done;
                 char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
 
-                __set_current_state(TASK_RUNNING);
-
                 /* cpu stop callbacks are not allowed to sleep */
                 preempt_disable();
 
@@ -290,88 +294,55 @@ repeat:
                                           ksym_buf), arg);
 
                 cpu_stop_signal_done(done, true);
-        } else
-                schedule();
-
-        goto repeat;
+                goto repeat;
+        }
 }
 
 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
 
-/* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */
-static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
-                                           unsigned long action, void *hcpu)
+static void cpu_stop_create(unsigned int cpu)
+{
+        sched_set_stop_task(cpu, per_cpu(cpu_stopper_task, cpu));
+}
+
+static void cpu_stop_park(unsigned int cpu)
 {
-        unsigned int cpu = (unsigned long)hcpu;
         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
-        struct task_struct *p;
-
-        switch (action & ~CPU_TASKS_FROZEN) {
-        case CPU_UP_PREPARE:
-                BUG_ON(stopper->thread || stopper->enabled ||
-                       !list_empty(&stopper->works));
-                p = kthread_create_on_node(cpu_stopper_thread,
-                                           stopper,
-                                           cpu_to_node(cpu),
-                                           "migration/%d", cpu);
-                if (IS_ERR(p))
-                        return notifier_from_errno(PTR_ERR(p));
-                get_task_struct(p);
-                kthread_bind(p, cpu);
-                sched_set_stop_task(cpu, p);
-                stopper->thread = p;
-                break;
-
-        case CPU_ONLINE:
-                /* strictly unnecessary, as first user will wake it */
-                wake_up_process(stopper->thread);
-                /* mark enabled */
-                spin_lock_irq(&stopper->lock);
-                stopper->enabled = true;
-                spin_unlock_irq(&stopper->lock);
-                break;
-
-#ifdef CONFIG_HOTPLUG_CPU
-        case CPU_UP_CANCELED:
-        case CPU_POST_DEAD:
-        {
-                struct cpu_stop_work *work;
-
-                sched_set_stop_task(cpu, NULL);
-                /* kill the stopper */
-                kthread_stop(stopper->thread);
-                /* drain remaining works */
-                spin_lock_irq(&stopper->lock);
-                list_for_each_entry(work, &stopper->works, list)
-                        cpu_stop_signal_done(work->done, false);
-                stopper->enabled = false;
-                spin_unlock_irq(&stopper->lock);
-                /* release the stopper */
-                put_task_struct(stopper->thread);
-                stopper->thread = NULL;
-                break;
-        }
-#endif
-        }
+        struct cpu_stop_work *work;
+        unsigned long flags;
 
-        return NOTIFY_OK;
+        /* drain remaining works */
+        spin_lock_irqsave(&stopper->lock, flags);
+        list_for_each_entry(work, &stopper->works, list)
+                cpu_stop_signal_done(work->done, false);
+        stopper->enabled = false;
+        spin_unlock_irqrestore(&stopper->lock, flags);
 }
 
-/*
- * Give it a higher priority so that cpu stopper is available to other
- * cpu notifiers.  It currently shares the same priority as sched
- * migration_notifier.
- */
-static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = {
-        .notifier_call  = cpu_stop_cpu_callback,
-        .priority       = 10,
+static void cpu_stop_unpark(unsigned int cpu)
+{
+        struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
+
+        spin_lock_irq(&stopper->lock);
+        stopper->enabled = true;
+        spin_unlock_irq(&stopper->lock);
+}
+
+static struct smp_hotplug_thread cpu_stop_threads = {
+        .store                  = &cpu_stopper_task,
+        .thread_should_run      = cpu_stop_should_run,
+        .thread_fn              = cpu_stopper_thread,
+        .thread_comm            = "migration/%u",
+        .create                 = cpu_stop_create,
+        .setup                  = cpu_stop_unpark,
+        .park                   = cpu_stop_park,
+        .unpark                 = cpu_stop_unpark,
+        .selfparking            = true,
 };
 
 static int __init cpu_stop_init(void)
 {
-        void *bcpu = (void *)(long)smp_processor_id();
         unsigned int cpu;
-        int err;
 
         for_each_possible_cpu(cpu) {
                 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
@@ -380,15 +351,8 @@ static int __init cpu_stop_init(void)
                 INIT_LIST_HEAD(&stopper->works);
         }
 
-        /* start one for the boot cpu */
-        err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
-                                    bcpu);
-        BUG_ON(err != NOTIFY_OK);
-        cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
-        register_cpu_notifier(&cpu_stop_cpu_notifier);
-
+        BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
         stop_machine_initialized = true;
-
         return 0;
 }
 early_initcall(cpu_stop_init);