smpboot: allow passing the cpumask on per-cpu thread registration

It makes the registration cheaper and simpler for the smpboot per-cpu
kthread users that don't need to always update the cpumask after threads
creation.

[sfr@canb.auug.org.au: fix for allow passing the cpumask on per-cpu thread registration]
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: Chris Metcalf <cmetcalf@ezchip.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/smpboot.h

@@ -48,7 +48,16 @@ struct smp_hotplug_thread {
 	const char			*thread_comm;
 };
 
-int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread);
+int smpboot_register_percpu_thread_cpumask(struct smp_hotplug_thread *plug_thread,
+					   const struct cpumask *cpumask);
+
+static inline int
+smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
+{
+	return smpboot_register_percpu_thread_cpumask(plug_thread,
+						      cpu_possible_mask);
+}
+
 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread);
 int smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread,
 					 const struct cpumask *);

kernel/smpboot.c

@@ -273,19 +273,22 @@ static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
 }
 
 /**
- * smpboot_register_percpu_thread - Register a per_cpu thread related to hotplug
+ * smpboot_register_percpu_thread_cpumask - Register a per_cpu thread related
+ * 					    to hotplug
  * @plug_thread:	Hotplug thread descriptor
+ * @cpumask:		The cpumask where threads run
  *
  * Creates and starts the threads on all online cpus.
  */
-int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
+int smpboot_register_percpu_thread_cpumask(struct smp_hotplug_thread *plug_thread,
+					   const struct cpumask *cpumask)
 {
 	unsigned int cpu;
 	int ret = 0;
 
 	if (!alloc_cpumask_var(&plug_thread->cpumask, GFP_KERNEL))
 		return -ENOMEM;
-	cpumask_copy(plug_thread->cpumask, cpu_possible_mask);
+	cpumask_copy(plug_thread->cpumask, cpumask);
 
 	get_online_cpus();
 	mutex_lock(&smpboot_threads_lock);
@@ -296,7 +299,8 @@ int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
 			free_cpumask_var(plug_thread->cpumask);
 			goto out;
 		}
-		smpboot_unpark_thread(plug_thread, cpu);
+		if (cpumask_test_cpu(cpu, cpumask))
+			smpboot_unpark_thread(plug_thread, cpu);
 	}
 	list_add(&plug_thread->list, &hotplug_threads);
 out:
@@ -304,7 +308,7 @@ out:
 	put_online_cpus();
 	return ret;
 }
-EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
+EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread_cpumask);
 
 /**
  * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug

kernel/watchdog.c

@@ -713,15 +713,12 @@ static int watchdog_enable_all_cpus(void)
 	int err = 0;
 
 	if (!watchdog_running) {
-		err = smpboot_register_percpu_thread(&watchdog_threads);
+		err = smpboot_register_percpu_thread_cpumask(&watchdog_threads,
+							     &watchdog_cpumask);
 		if (err)
 			pr_err("Failed to create watchdog threads, disabled\n");
-		else {
-			if (smpboot_update_cpumask_percpu_thread(
-				    &watchdog_threads, &watchdog_cpumask))
-				pr_err("Failed to set cpumask for watchdog threads\n");
+		else
 			watchdog_running = 1;
-		}
 	} else {
 		/*
 		 * Enable/disable the lockup detectors or