Merge git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-for-linus

* git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-for-linus:
  work_on_cpu(): rewrite it to create a kernel thread on demand
  kthread: move sched-realeted initialization from kthreadd context
  kthread: Don't looking for a task in create_kthread() #2

kernel/kthread.c

@@ -76,6 +76,7 @@ static int kthread(void *_create)
 
 	/* OK, tell user we're spawned, wait for stop or wakeup */
 	__set_current_state(TASK_UNINTERRUPTIBLE);
+	create->result = current;
 	complete(&create->started);
 	schedule();
 
@@ -96,22 +97,10 @@ static void create_kthread(struct kthread_create_info *create)
 
 	/* We want our own signal handler (we take no signals by default). */
 	pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
-	if (pid < 0) {
+	if (pid < 0)
 		create->result = ERR_PTR(pid);
-	} else {
-		struct sched_param param = { .sched_priority = 0 };
+	else
 		wait_for_completion(&create->started);
-		read_lock(&tasklist_lock);
-		create->result = find_task_by_pid_ns(pid, &init_pid_ns);
-		read_unlock(&tasklist_lock);
-		/*
-		 * root may have changed our (kthreadd's) priority or CPU mask.
-		 * The kernel thread should not inherit these properties.
-		 */
-		sched_setscheduler(create->result, SCHED_NORMAL, &param);
-		set_user_nice(create->result, KTHREAD_NICE_LEVEL);
-		set_cpus_allowed_ptr(create->result, cpu_all_mask);
-	}
 	complete(&create->done);
 }
 
@@ -154,11 +143,20 @@ struct task_struct *kthread_create(int (*threadfn)(void *data),
 	wait_for_completion(&create.done);
 
 	if (!IS_ERR(create.result)) {
+		struct sched_param param = { .sched_priority = 0 };
 		va_list args;
+
 		va_start(args, namefmt);
 		vsnprintf(create.result->comm, sizeof(create.result->comm),
 			  namefmt, args);
 		va_end(args);
+		/*
+		 * root may have changed our (kthreadd's) priority or CPU mask.
+		 * The kernel thread should not inherit these properties.
+		 */
+		sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
+		set_user_nice(create.result, KTHREAD_NICE_LEVEL);
+		set_cpus_allowed_ptr(create.result, cpu_all_mask);
 	}
 	return create.result;
 }

kernel/workqueue.c

@@ -966,20 +966,20 @@ undo:
 }
 
 #ifdef CONFIG_SMP
-static struct workqueue_struct *work_on_cpu_wq __read_mostly;
 
 struct work_for_cpu {
-	struct work_struct work;
+	struct completion completion;
 	long (*fn)(void *);
 	void *arg;
 	long ret;
 };
 
-static void do_work_for_cpu(struct work_struct *w)
+static int do_work_for_cpu(void *_wfc)
 {
-	struct work_for_cpu *wfc = container_of(w, struct work_for_cpu, work);
-
+	struct work_for_cpu *wfc = _wfc;
 	wfc->ret = wfc->fn(wfc->arg);
+	complete(&wfc->completion);
+	return 0;
 }
 
 /**
@@ -990,17 +990,23 @@ static void do_work_for_cpu(struct work_struct *w)
  *
  * This will return the value @fn returns.
  * It is up to the caller to ensure that the cpu doesn't go offline.
+ * The caller must not hold any locks which would prevent @fn from completing.
  */
 long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg)
 {
-	struct work_for_cpu wfc;
-
-	INIT_WORK(&wfc.work, do_work_for_cpu);
-	wfc.fn = fn;
-	wfc.arg = arg;
-	queue_work_on(cpu, work_on_cpu_wq, &wfc.work);
-	flush_work(&wfc.work);
-
+	struct task_struct *sub_thread;
+	struct work_for_cpu wfc = {
+		.completion = COMPLETION_INITIALIZER_ONSTACK(wfc.completion),
+		.fn = fn,
+		.arg = arg,
+	};
+
+	sub_thread = kthread_create(do_work_for_cpu, &wfc, "work_for_cpu");
+	if (IS_ERR(sub_thread))
+		return PTR_ERR(sub_thread);
+	kthread_bind(sub_thread, cpu);
+	wake_up_process(sub_thread);
+	wait_for_completion(&wfc.completion);
 	return wfc.ret;
 }
 EXPORT_SYMBOL_GPL(work_on_cpu);
@@ -1016,8 +1022,4 @@ void __init init_workqueues(void)
 	hotcpu_notifier(workqueue_cpu_callback, 0);
 	keventd_wq = create_workqueue("events");
 	BUG_ON(!keventd_wq);
-#ifdef CONFIG_SMP
-	work_on_cpu_wq = create_workqueue("work_on_cpu");
-	BUG_ON(!work_on_cpu_wq);
-#endif
 }