4 files changed, 285 insertions, 1 deletions

diff --git a/include/linux/smpboot.h b/include/linux/smpboot.h
new file mode 100644
index 000000000000..e0106d8581d3
--- /dev/null
+++ b/include/linux/smpboot.h
@@ -0,0 +1,43 @@
+#ifndef _LINUX_SMPBOOT_H
+#define _LINUX_SMPBOOT_H
+
+#include <linux/types.h>
+
+struct task_struct;
+/* Cookie handed to the thread_fn*/
+struct smpboot_thread_data;
+
+/**
+ * struct smp_hotplug_thread - CPU hotplug related thread descriptor
+ * @store:              Pointer to per cpu storage for the task pointers
+ * @list:               List head for core management
+ * @thread_should_run:  Check whether the thread should run or not. Called with
+ *                      preemption disabled.
+ * @thread_fn:          The associated thread function
+ * @setup:              Optional setup function, called when the thread gets
+ *                      operational the first time
+ * @cleanup:            Optional cleanup function, called when the thread
+ *                      should stop (module exit)
+ * @park:               Optional park function, called when the thread is
+ *                      parked (cpu offline)
+ * @unpark:             Optional unpark function, called when the thread is
+ *                      unparked (cpu online)
+ * @thread_comm:        The base name of the thread
+ */
+struct smp_hotplug_thread {
+        struct task_struct __percpu     **store;
+        struct list_head                list;
+        int                             (*thread_should_run)(unsigned int cpu);
+        void                            (*thread_fn)(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);
+        const char                      *thread_comm;
+};
+
+int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread);
+void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread);
+int smpboot_thread_schedule(void);
+
+#endif
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 14d32588cccd..e615dfbcf794 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -280,12 +280,13 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
                                 __func__, cpu);
                 goto out_release;
         }
+        smpboot_park_threads(cpu);
 
         err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
         if (err) {
                 /* CPU didn't die: tell everyone.  Can't complain. */
+                smpboot_unpark_threads(cpu);
                 cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
-
                 goto out_release;
         }
         BUG_ON(cpu_online(cpu));
@@ -354,6 +355,10 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
                 goto out;
         }
 
+        ret = smpboot_create_threads(cpu);
+        if (ret)
+                goto out;
+
         ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls);
         if (ret) {
                 nr_calls--;
@@ -368,6 +373,9 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
                 goto out_notify;
         BUG_ON(!cpu_online(cpu));
 
+        /* Wake the per cpu threads */
+        smpboot_unpark_threads(cpu);
+
         /* Now call notifier in preparation. */
         cpu_notify(CPU_ONLINE | mod, hcpu);
 
diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 98f60c5caa1b..9d5f7b04025d 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -1,11 +1,17 @@
 /*
  * Common SMP CPU bringup/teardown functions
  */
+#include <linux/cpu.h>
 #include <linux/err.h>
 #include <linux/smp.h>
 #include <linux/init.h>
+#include <linux/list.h>
+#include <linux/slab.h>
 #include <linux/sched.h>
+#include <linux/export.h>
 #include <linux/percpu.h>
+#include <linux/kthread.h>
+#include <linux/smpboot.h>
 
 #include "smpboot.h"
 
@@ -65,3 +71,226 @@ void __init idle_threads_init(void)
         }
 }
 #endif
+
+static LIST_HEAD(hotplug_threads);
+static DEFINE_MUTEX(smpboot_threads_lock);
+
+struct smpboot_thread_data {
+        unsigned int                    cpu;
+        unsigned int                    status;
+        struct smp_hotplug_thread       *ht;
+};
+
+enum {
+        HP_THREAD_NONE = 0,
+        HP_THREAD_ACTIVE,
+        HP_THREAD_PARKED,
+};
+
+/**
+ * smpboot_thread_fn - percpu hotplug thread loop function
+ * @data:       thread data pointer
+ *
+ * Checks for thread stop and park conditions. Calls the necessary
+ * setup, cleanup, park and unpark functions for the registered
+ * thread.
+ *
+ * Returns 1 when the thread should exit, 0 otherwise.
+ */
+static int smpboot_thread_fn(void *data)
+{
+        struct smpboot_thread_data *td = data;
+        struct smp_hotplug_thread *ht = td->ht;
+
+        while (1) {
+                set_current_state(TASK_INTERRUPTIBLE);
+                preempt_disable();
+                if (kthread_should_stop()) {
+                        set_current_state(TASK_RUNNING);
+                        preempt_enable();
+                        if (ht->cleanup)
+                                ht->cleanup(td->cpu, cpu_online(td->cpu));
+                        kfree(td);
+                        return 0;
+                }
+
+                if (kthread_should_park()) {
+                        __set_current_state(TASK_RUNNING);
+                        preempt_enable();
+                        if (ht->park && td->status == HP_THREAD_ACTIVE) {
+                                BUG_ON(td->cpu != smp_processor_id());
+                                ht->park(td->cpu);
+                                td->status = HP_THREAD_PARKED;
+                        }
+                        kthread_parkme();
+                        /* We might have been woken for stop */
+                        continue;
+                }
+
+                BUG_ON(td->cpu != smp_processor_id());
+
+                /* Check for state change setup */
+                switch (td->status) {
+                case HP_THREAD_NONE:
+                        preempt_enable();
+                        if (ht->setup)
+                                ht->setup(td->cpu);
+                        td->status = HP_THREAD_ACTIVE;
+                        preempt_disable();
+                        break;
+                case HP_THREAD_PARKED:
+                        preempt_enable();
+                        if (ht->unpark)
+                                ht->unpark(td->cpu);
+                        td->status = HP_THREAD_ACTIVE;
+                        preempt_disable();
+                        break;
+                }
+
+                if (!ht->thread_should_run(td->cpu)) {
+                        preempt_enable();
+                        schedule();
+                } else {
+                        set_current_state(TASK_RUNNING);
+                        preempt_enable();
+                        ht->thread_fn(td->cpu);
+                }
+        }
+}
+
+static int
+__smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
+{
+        struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
+        struct smpboot_thread_data *td;
+
+        if (tsk)
+                return 0;
+
+        td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
+        if (!td)
+                return -ENOMEM;
+        td->cpu = cpu;
+        td->ht = ht;
+
+        tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
+                                    ht->thread_comm);
+        if (IS_ERR(tsk)) {
+                kfree(td);
+                return PTR_ERR(tsk);
+        }
+
+        get_task_struct(tsk);
+        *per_cpu_ptr(ht->store, cpu) = tsk;
+        return 0;
+}
+
+int smpboot_create_threads(unsigned int cpu)
+{
+        struct smp_hotplug_thread *cur;
+        int ret = 0;
+
+        mutex_lock(&smpboot_threads_lock);
+        list_for_each_entry(cur, &hotplug_threads, list) {
+                ret = __smpboot_create_thread(cur, cpu);
+                if (ret)
+                        break;
+        }
+        mutex_unlock(&smpboot_threads_lock);
+        return ret;
+}
+
+static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
+{
+        struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
+
+        kthread_unpark(tsk);
+}
+
+void smpboot_unpark_threads(unsigned int cpu)
+{
+        struct smp_hotplug_thread *cur;
+
+        mutex_lock(&smpboot_threads_lock);
+        list_for_each_entry(cur, &hotplug_threads, list)
+                smpboot_unpark_thread(cur, cpu);
+        mutex_unlock(&smpboot_threads_lock);
+}
+
+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)
+                kthread_park(tsk);
+}
+
+void smpboot_park_threads(unsigned int cpu)
+{
+        struct smp_hotplug_thread *cur;
+
+        mutex_lock(&smpboot_threads_lock);
+        list_for_each_entry_reverse(cur, &hotplug_threads, list)
+                smpboot_park_thread(cur, cpu);
+        mutex_unlock(&smpboot_threads_lock);
+}
+
+static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
+{
+        unsigned int cpu;
+
+        /* We need to destroy also the parked threads of offline cpus */
+        for_each_possible_cpu(cpu) {
+                struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
+
+                if (tsk) {
+                        kthread_stop(tsk);
+                        put_task_struct(tsk);
+                        *per_cpu_ptr(ht->store, cpu) = NULL;
+                }
+        }
+}
+
+/**
+ * smpboot_register_percpu_thread - Register a per_cpu thread related to hotplug
+ * @plug_thread:        Hotplug thread descriptor
+ *
+ * Creates and starts the threads on all online cpus.
+ */
+int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
+{
+        unsigned int cpu;
+        int ret = 0;
+
+        mutex_lock(&smpboot_threads_lock);
+        for_each_online_cpu(cpu) {
+                ret = __smpboot_create_thread(plug_thread, cpu);
+                if (ret) {
+                        smpboot_destroy_threads(plug_thread);
+                        goto out;
+                }
+                smpboot_unpark_thread(plug_thread, cpu);
+        }
+        list_add(&plug_thread->list, &hotplug_threads);
+out:
+        mutex_unlock(&smpboot_threads_lock);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
+
+/**
+ * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
+ * @plug_thread:        Hotplug thread descriptor
+ *
+ * Stops all threads on all possible cpus.
+ */
+void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
+{
+        get_online_cpus();
+        mutex_lock(&smpboot_threads_lock);
+        list_del(&plug_thread->list);
+        smpboot_destroy_threads(plug_thread);
+        mutex_unlock(&smpboot_threads_lock);
+        put_online_cpus();
+}
+EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
diff --git a/kernel/smpboot.h b/kernel/smpboot.h
index 6ef9433e1c70..72415a0eb955 100644
--- a/kernel/smpboot.h
+++ b/kernel/smpboot.h
@@ -13,4 +13,8 @@ static inline void idle_thread_set_boot_cpu(void) { }
 static inline void idle_threads_init(void) { }
 #endif
 
+int smpboot_create_threads(unsigned int cpu);
+void smpboot_park_threads(unsigned int cpu);
+void smpboot_unpark_threads(unsigned int cpu);
+
 #endif