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>

3 files changed, 22 insertions, 12 deletions

diff --git a/include/linux/smpboot.h b/include/linux/smpboot.h
index da3c593f9845..e6109a6cd8f6 100644
--- a/include/linux/smpboot.h
+++ b/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 *);
diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 60aa858a6a07..a818cbc73e14 100644
--- a/kernel/smpboot.c
+++ b/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
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index a6ffa43f2993..e5bb86fb0ea5 100644
--- a/kernel/watchdog.c
+++ b/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