smpboot: Allow selfparking per cpu threads

The stop machine threads are still killed when a cpu goes offline. The
reason is that the thread is used to bring the cpu down, so it can't
be parked along with the other per cpu threads.

Allow a per cpu thread to be excluded from automatic parking, so it
can park itself once it's done

Add a create callback function as well.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Arjan van de Veen <arjan@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Richard Weinberger <rw@linutronix.de>
Cc: Magnus Damm <magnus.damm@gmail.com>
Link: http://lkml.kernel.org/r/20130131120741.553993267@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

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;
 };
 

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);
 }