Update device model locking

Change all iterators of devices to:
- use list_for_each
- check return of get_device_locked
- don't break until we hold the lock if we get an error

When a device's reference count hits 0, remove it from all lists, including
bus and driver lists.

Between the iterator algorithm and the guaranteed removal from the lists,
there should never be a device in a list with a reference count of 0. 
So, whenever we're iterating over the lists, we'll always have a valid 
device. We don't decrement the refcount until the next iteration of the
loop, so we're also guaranteed to get the correct next item in the list.

drivers/base/bus.c

@@ -16,6 +16,9 @@
 
 static LIST_HEAD(bus_driver_list);
 
+#define to_dev(node) container_of(node,struct device,bus_list)
+#define to_drv(node) container_of(node,struct device_driver,bus_list)
+
 /**
  * bus_for_each_dev - walk list of devices and do something to each
  * @bus:	bus in question
@@ -26,42 +29,41 @@ static LIST_HEAD(bus_driver_list);
  * counting on devices as we touch each one.
  *
  * Algorithm:
- * Take the bus lock and get the first node in the list. We increment
- * the reference count and unlock the bus. If we have a device from a 
- * previous iteration, we decrement the reference count. 
- * After we call the callback, we get the next node in the list and loop.
- * At the end, if @dev is not null, we still have it pinned, so we need
- * to let it go.
+ * Take device_lock and get the first node in the list. 
+ * Try and increment the reference count on it. If we can't, it's in the
+ * process of being removed, but that process hasn't acquired device_lock.
+ * It's still in the list, so we grab the next node and try that one. 
+ * We drop the lock to call the callback.
+ * We can't decrement the reference count yet, because we need the next
+ * node in the list. So, we set @prev to point to the current device.
+ * On the next go-round, we decrement the reference count on @prev, so if 
+ * it's being removed, it won't affect us.
  */
 int bus_for_each_dev(struct bus_type * bus, void * data, 
 		     int (*callback)(struct device * dev, void * data))
 {
-	struct device * next;
-	struct device * dev = NULL;
 	struct list_head * node;
+	struct device * prev = NULL;
 	int error = 0;
 
 	get_bus(bus);
 	spin_lock(&device_lock);
-	node = bus->devices.next;
-	while (node != &bus->devices) {
-		next = list_entry(node,struct device,bus_list);
-		get_device_locked(next);
-		spin_unlock(&device_lock);
-
-		if (dev)
-			put_device(dev);
-		dev = next;
-		if ((error = callback(dev,data))) {
-			put_device(dev);
-			break;
+	list_for_each(node,&bus->devices) {
+		struct device * dev = get_device_locked(to_dev(node));
+		if (dev) {
+			spin_unlock(&device_lock);
+			error = callback(dev,data);
+			if (prev)
+				put_device(prev);
+			prev = dev;
+			spin_lock(&device_lock);
+			if (error)
+				break;
 		}
-		spin_lock(&device_lock);
-		node = dev->bus_list.next;
 	}
 	spin_unlock(&device_lock);
-	if (dev)
-		put_device(dev);
+	if (prev)
+		put_device(prev);
 	put_bus(bus);
 	return error;
 }
@@ -69,34 +71,30 @@ int bus_for_each_dev(struct bus_type * bus, void * data,
 int bus_for_each_drv(struct bus_type * bus, void * data,
 		     int (*callback)(struct device_driver * drv, void * data))
 {
-	struct device_driver * next;
-	struct device_driver * drv = NULL;
 	struct list_head * node;
+	struct device_driver * prev = NULL;
 	int error = 0;
 
 	/* pin bus in memory */
 	get_bus(bus);
 
 	spin_lock(&device_lock);
-	node = bus->drivers.next;
-	while (node != &bus->drivers) {
-		next = list_entry(node,struct device_driver,bus_list);
-		get_driver(next);
-		spin_unlock(&device_lock);
-
-		if (drv)
-			put_driver(drv);
-		drv = next;
-		if ((error = callback(drv,data))) {
-			put_driver(drv);
-			break;
+	list_for_each(node,&bus->drivers) {
+		struct device_driver * drv = get_driver(to_drv(node));
+		if (drv) {
+			spin_unlock(&device_lock);
+			error = callback(drv,data);
+			if (prev)
+				put_driver(prev);
+			prev = drv;
+			spin_lock(&device_lock);
+			if (error)
+				break;
 		}
-		spin_lock(&device_lock);
-		node = drv->bus_list.next;
 	}
 	spin_unlock(&device_lock);
-	if (drv)
-		put_driver(drv);
+	if (prev)
+		put_driver(prev);
 	put_bus(bus);
 	return error;
 }
@@ -134,9 +132,6 @@ void bus_remove_device(struct device * dev)
 {
 	if (dev->bus) {
 		device_remove_symlink(&dev->bus->device_dir,dev->bus_id);
-		spin_lock(&device_lock);
-		list_del_init(&dev->bus_list);
-		spin_unlock(&device_lock);
 		put_bus(dev->bus);
 	}
 }

drivers/base/core.c

@@ -25,6 +25,8 @@ int (*platform_notify_remove)(struct device * dev) = NULL;
 
 spinlock_t device_lock = SPIN_LOCK_UNLOCKED;
 
+#define to_dev(node) container_of(node,struct device,driver_list)
+
 
 /**
  * found_match - do actual binding of device to driver
@@ -101,14 +103,10 @@ static void device_detach(struct device * dev)
 	struct device_driver * drv; 
 
 	if (dev->driver) {
-		lock_device(dev);
+		spin_lock(&device_lock);
 		drv = dev->driver;
 		dev->driver = NULL;
-		unlock_device(dev);
-
-		write_lock(&drv->lock);
-		list_del_init(&dev->driver_list);
-		write_unlock(&drv->lock);
+		spin_unlock(&device_lock);
 
 		/* detach from driver */
 		if (drv->remove)
@@ -136,45 +134,37 @@ int driver_attach(struct device_driver * drv)
 
 static int do_driver_detach(struct device * dev, struct device_driver * drv)
 {
-	lock_device(dev);
+	spin_lock(&device_lock);
 	if (dev->driver == drv) {
 		dev->driver = NULL;
-		unlock_device(dev);
+		spin_unlock(&device_lock);
+
 		if (drv->remove)
 			drv->remove(dev);
 	} else
-		unlock_device(dev);
+		spin_unlock(&device_lock);
 	return 0;
 }
 
 void driver_detach(struct device_driver * drv)
 {
-	struct device * next;
-	struct device * dev = NULL;
 	struct list_head * node;
-	int error = 0;
+	struct device * prev = NULL;
 
 	spin_lock(&device_lock);
-	node = drv->devices.next;
-	while (node != &drv->devices) {
-		next = list_entry(node,struct device,driver_list);
-		get_device_locked(next);
-		list_del_init(&next->driver_list);
-		spin_unlock(&device_lock);
-
-		if (dev)
-			put_device(dev);
-		dev = next;
-		if ((error = do_driver_detach(dev,drv))) {
-			put_device(dev);
-			break;
+	list_for_each(node,&drv->devices) {
+		struct device * dev = get_device_locked(to_dev(node));
+		if (dev) {
+			list_del_init(node);
+			spin_unlock(&device_lock);
+			do_driver_detach(dev,drv);
+			if (prev)
+				put_device(prev);
+			prev = dev;
+			spin_lock(&device_lock);
 		}
-		spin_lock(&device_lock);
-		node = drv->devices.next;
 	}
 	spin_unlock(&device_lock);
-	if (dev)
-		put_device(dev);
 }
 
 /**
@@ -245,7 +235,7 @@ int device_register(struct device *dev)
 struct device * get_device_locked(struct device * dev)
 {
 	struct device * ret = dev;
-	if (dev && atomic_read(&dev->refcount))
+	if (dev && atomic_read(&dev->refcount) > 0)
 		atomic_inc(&dev->refcount);
 	else
 		ret = NULL;
@@ -271,6 +261,8 @@ void put_device(struct device * dev)
 		return;
 	list_del_init(&dev->node);
 	list_del_init(&dev->g_list);
+	list_del_init(&dev->bus_list);
+	list_del_init(&dev->driver_list);
 	spin_unlock(&device_lock);
 
 	pr_debug("DEV: Unregistering device. ID = '%s', name = '%s'\n",

drivers/base/driver.c

@@ -10,35 +10,31 @@
 #include <linux/errno.h>
 #include "base.h"
 
+#define to_dev(node) container_of(node,struct device,driver_list)
 
-int driver_for_each_dev(struct device_driver * drv, void * data, int (*callback)(struct device *, void * ))
+int driver_for_each_dev(struct device_driver * drv, void * data, 
+			int (*callback)(struct device *, void * ))
 {
-	struct device * next;
-	struct device * dev = NULL;
 	struct list_head * node;
+	struct device * prev = NULL;
 	int error = 0;
 
 	get_driver(drv);
 	spin_lock(&device_lock);
-	node = drv->devices.next;
-	while (node != &drv->devices) {
-		next = list_entry(node,struct device,driver_list);
-		get_device_locked(next);
-		spin_unlock(&device_lock);
-
-		if (dev)
-			put_device(dev);
-		dev = next;
-		if ((error = callback(dev,data))) {
-			put_device(dev);
-			break;
+	list_for_each(node,&drv->devices) {
+		struct device * dev = get_device_locked(to_dev(node));
+		if (dev) {
+			spin_unlock(&device_lock);
+			error = callback(dev,data);
+			if (prev)
+				put_device(prev);
+			prev = dev;
+			spin_lock(&device_lock);
+			if (error)
+				break;
 		}
-		spin_lock(&device_lock);
-		node = dev->driver_list.next;
 	}
 	spin_unlock(&device_lock);
-	if (dev)
-		put_device(dev);
 	put_driver(drv);
 	return error;
 }

drivers/base/power.c

@@ -14,6 +14,8 @@
 #include <linux/module.h>
 #include "base.h"
 
+#define to_dev(node) container_of(node,struct device,g_list)
+
 /**
  * device_suspend - suspend all devices on the device tree
  * @state:	state we're entering
@@ -25,30 +27,26 @@
  */
 int device_suspend(u32 state, u32 level)
 {
-	struct device * dev;
-	struct device * prev = &device_root;
+	struct list_head * node;
+	struct device * prev = NULL;
 	int error = 0;
 
 	printk(KERN_EMERG "Suspending Devices\n");
 
-	get_device(prev);
-
 	spin_lock(&device_lock);
-	dev = g_list_to_dev(prev->g_list.next);
-	while(dev != &device_root && !error) {
-		get_device_locked(dev);
-		spin_unlock(&device_lock);
-		put_device(prev);
-
-		if (dev->driver && dev->driver->suspend)
-			error = dev->driver->suspend(dev,state,level);
-
-		spin_lock(&device_lock);
-		prev = dev;
-		dev = g_list_to_dev(prev->g_list.next);
+	list_for_each(node,&device_root.g_list) {
+		struct device * dev = get_device_locked(dev);
+		if (dev) {
+			spin_unlock(&device_lock);
+			if (dev->driver && dev->driver->suspend)
+				error = dev->driver->suspend(dev,state,level);
+			if (prev)
+				put_device(prev);
+			prev = dev;
+			spin_lock(&device_lock);
+		}
 	}
 	spin_unlock(&device_lock);
-	put_device(prev);
 
 	return error;
 }
@@ -63,27 +61,23 @@ int device_suspend(u32 state, u32 level)
  */
 void device_resume(u32 level)
 {
-	struct device * dev;
-	struct device * prev = &device_root;
-
-	get_device(prev);
+	struct list_head * node;
+	struct device * prev = NULL;
 
 	spin_lock(&device_lock);
-	dev = g_list_to_dev(prev->g_list.prev);
-	while(dev != &device_root) {
-		get_device_locked(dev);
-		spin_unlock(&device_lock);
-		put_device(prev);
-
-		if (dev->driver && dev->driver->resume)
-			dev->driver->resume(dev,level);
-
-		spin_lock(&device_lock);
-		prev = dev;
-		dev = g_list_to_dev(prev->g_list.prev);
+	list_for_each_prev(node,&device_root.g_list) {
+		struct device * dev = get_device_locked(to_dev(node));
+		if (dev) {
+			spin_unlock(&device_lock);
+			if (dev->driver && dev->driver->resume)
+				dev->driver->resume(dev,level);
+			if (prev)
+				put_device(prev);
+			prev = dev;
+			spin_lock(&device_lock);
+		}
 	}
 	spin_unlock(&device_lock);
-	put_device(prev);
 
 	printk(KERN_EMERG "Devices Resumed\n");
 }
@@ -98,29 +92,25 @@ void device_resume(u32 level)
  */
 void device_shutdown(void)
 {
-	struct device * dev;
-	struct device * prev = &device_root;
+	struct list_head * node;
+	struct device * prev = NULL;
 
 	printk(KERN_EMERG "Shutting down devices\n");
 
-	get_device(prev);
-
 	spin_lock(&device_lock);
-	dev = g_list_to_dev(prev->g_list.next);
-	while(dev != &device_root) {
-		dev = get_device_locked(dev);
-		spin_unlock(&device_lock);
-		put_device(prev);
-
-		if (dev->driver && dev->driver->remove)
-			dev->driver->remove(dev);
-
-		spin_lock(&device_lock);
-		prev = dev;
-		dev = g_list_to_dev(prev->g_list.next);
+	list_for_each(node,&device_root.g_list) {
+		struct device * dev = get_device_locked(to_dev(node));
+		if (dev) {
+			spin_unlock(&device_lock);
+			if (dev->driver && dev->driver->remove)
+				dev->driver->remove(dev);
+			if (prev)
+				put_device(prev);
+			prev = dev;
+			spin_lock(&device_lock);
+		}
 	}
 	spin_unlock(&device_lock);
-	put_device(prev);
 }
 
 EXPORT_SYMBOL(device_suspend);