Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm1-V0.7.28-1

[Ingo Molnar <mingo@elte.hu>]

* Rui Nuno Capela <rncbc@rncbc.org> wrote:

> I'm still seeing this sometimes (not everytime) on my P4/UP laptop
> while shutting down ALSA modules. This isn't the same as the lockup
> I've been reporting lately (that happens on my P4/SMT desktop) but may
> be remotely related.

could you (and Christian) try the patch below, ontop of a current-ish
tree - does the unload crash still occur? (this is an earlier cleanup
patch from Thomas Gleixner, but it could fix a real PREEMPT_RT bug in
this particular case.)

	Ingo

--- linux/drivers/base/driver.c.orig
+++ linux/drivers/base/driver.c
@@ -79,14 +79,13 @@ void put_driver(struct device_driver * d
  *	since most of the things we have to do deal with the bus
  *	structures.
  *
- *	The one interesting aspect is that we initialize @drv->unload_sem
- *	to a locked state here. It will be unlocked when the driver
- *	reference count reaches 0.
+ *	We init the completion strcut here. When the reference 
+ *	count reaches zero, complete() is called from bus_release().
  */
 int driver_register(struct device_driver * drv)
 {
 	INIT_LIST_HEAD(&drv->devices);
-	init_MUTEX_LOCKED(&drv->unload_sem);
+	init_completion(&drv->unload_done);
 	return bus_add_driver(drv);
 }
 
@@ -97,18 +96,16 @@ int driver_register(struct device_driver
  *
  *	Again, we pass off most of the work to the bus-level call.
  *
- *	Though, once that is done, we attempt to take @drv->unload_sem.
- *	This will block until the driver refcount reaches 0, and it is
- *	released. Only modular drivers will call this function, and we
+ *	Though, once that is done, we wait until the driver refcount 
+ *	reaches 0, and complete() is called in bus_release().
+ *	Only modular drivers will call this function, and we
  *	have to guarantee that it won't complete, letting the driver
  *	unload until all references are gone.
  */
-
 void driver_unregister(struct device_driver * drv)
 {
 	bus_remove_driver(drv);
-	down(&drv->unload_sem);
-	up(&drv->unload_sem);
+	wait_for_completion(&drv->unload_done);
 }
 
 /**
--- linux/drivers/base/bus.c.orig
+++ linux/drivers/base/bus.c
@@ -65,7 +65,7 @@ static struct sysfs_ops driver_sysfs_ops
 static void driver_release(struct kobject * kobj)
 {
 	struct device_driver * drv = to_driver(kobj);
-	up(&drv->unload_sem);
+	complete(&drv->unload_done);
 }
 
 static struct kobj_type ktype_driver = {
--- linux/include/linux/device.h.orig
+++ linux/include/linux/device.h
@@ -102,7 +102,7 @@ struct device_driver {
 	char			* name;
 	struct bus_type		* bus;
 
-	struct semaphore	unload_sem;
+	struct completion	unload_done;
 	struct kobject		kobj;
 	struct list_head	devices;