[PATCH 1/2] driver core: class: implement class_get/put without the private pointer.

[PATCH 1/2] driver core: class: implement class_get/put without the private pointer.

[Greg Kroah-Hartman]

Much like what was done in commit 273afac615ad ("driver core: bus:
implement bus_get/put() without the private pointer"), it is time to
move the driver core away from using the internal private pointer in
struct class in order to enable it to be always a constant and be placed
in read-only memory in the future.

First step in doing this is to create a helper function that turns a
'struct class' into 'struct subsys_private' called class_to_subsys().

class_to_subsys() walks the list of registered busses in the system and
finds the matching one based on the pointer to the class itself.  As
this is a short list, and this function is not on any fast path, it
should not be noticable.

Implement class_get() and class_put() using this new helper function.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/base/class.c | 81 ++++++++++++++++++++++++++++++++++----------
 1 file changed, 63 insertions(+), 18 deletions(-)

diff --git a/drivers/base/class.c b/drivers/base/class.c
index ecbf8b5b0dff..90678f6ed4ba 100644
--- a/drivers/base/class.c
+++ b/drivers/base/class.c
@@ -20,8 +20,70 @@
 #include <linux/mutex.h>
 #include "base.h"
 
+/* /sys/class */
+static struct kset *class_kset;
+
 #define to_class_attr(_attr) container_of(_attr, struct class_attribute, attr)
 
+/**
+ * class_to_subsys - Turn a struct class into a struct subsys_private
+ *
+ * @class: pointer to the struct bus_type to look up
+ *
+ * The driver core internals need to work on the subsys_private structure, not
+ * the external struct class pointer.  This function walks the list of
+ * registered classes in the system and finds the matching one and returns the
+ * internal struct subsys_private that relates to that class.
+ *
+ * Note, the reference count of the return value is INCREMENTED if it is not
+ * NULL.  A call to subsys_put() must be done when finished with the pointer in
+ * order for it to be properly freed.
+ */
+static struct subsys_private *class_to_subsys(const struct class *class)
+{
+	struct subsys_private *sp = NULL;
+	struct kobject *kobj;
+
+	if (!class || !class_kset)
+		return NULL;
+
+	spin_lock(&class_kset->list_lock);
+
+	if (list_empty(&class_kset->list))
+		goto done;
+
+	list_for_each_entry(kobj, &class_kset->list, entry) {
+		struct kset *kset = container_of(kobj, struct kset, kobj);
+
+		sp = container_of_const(kset, struct subsys_private, subsys);
+		if (sp->class == class)
+			goto done;
+	}
+	sp = NULL;
+done:
+	sp = subsys_get(sp);
+	spin_unlock(&class_kset->list_lock);
+	return sp;
+}
+
+static const struct class *class_get(const struct class *class)
+{
+	struct subsys_private *sp = class_to_subsys(class);
+
+	if (sp)
+		return class;
+	return NULL;
+}
+
+static void class_put(const struct class *class)
+{
+	struct subsys_private *sp = class_to_subsys(class);
+
+	/* two puts are required as the call to bus_to_subsys incremented it again */
+	subsys_put(sp);
+	subsys_put(sp);
+}
+
 static ssize_t class_attr_show(struct kobject *kobj, struct attribute *attr,
 			       char *buf)
 {
@@ -83,10 +145,6 @@ static const struct kobj_type class_ktype = {
 	.child_ns_type	= class_child_ns_type,
 };
 
-/* Hotplug events for classes go to the class subsys */
-static struct kset *class_kset;
-
-
 int class_create_file_ns(const struct class *cls, const struct class_attribute *attr,
 			 const void *ns)
 {
@@ -109,19 +167,6 @@ void class_remove_file_ns(const struct class *cls, const struct class_attribute
 }
 EXPORT_SYMBOL_GPL(class_remove_file_ns);
 
-static struct class *class_get(struct class *cls)
-{
-	if (cls)
-		kset_get(&cls->p->subsys);
-	return cls;
-}
-
-static void class_put(struct class *cls)
-{
-	if (cls)
-		kset_put(&cls->p->subsys);
-}
-
 static struct device *klist_class_to_dev(struct klist_node *n)
 {
 	struct device_private *p = to_device_private_class(n);
@@ -435,7 +480,7 @@ EXPORT_SYMBOL_GPL(class_find_device);
 
 int class_interface_register(struct class_interface *class_intf)
 {
-	struct class *parent;
+	const struct class *parent;
 	struct class_dev_iter iter;
 	struct device *dev;
 
-- 
2.40.0

[PATCH 2/2] driver core: class.c: convert to only use class_to_subsys

[Greg Kroah-Hartman]

Now that class_to_subsys() can be used to get access to the internal
class private pointer, convert the remaining few places in class.c that
were accessing the pointer directly to use class_to_subsys() instead.

By doing this, the need for class_get() and class_put() goes away as no
one actually tries to increment the class structures anymore, only the
internal dynamic one.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/base/class.c | 113 +++++++++++++++++++++++--------------------
 1 file changed, 61 insertions(+), 52 deletions(-)

diff --git a/drivers/base/class.c b/drivers/base/class.c
index 90678f6ed4ba..45d66a4fb375 100644
--- a/drivers/base/class.c
+++ b/drivers/base/class.c
@@ -66,24 +66,6 @@ static struct subsys_private *class_to_subsys(const struct class *class)
 	return sp;
 }
 
-static const struct class *class_get(const struct class *class)
-{
-	struct subsys_private *sp = class_to_subsys(class);
-
-	if (sp)
-		return class;
-	return NULL;
-}
-
-static void class_put(const struct class *class)
-{
-	struct subsys_private *sp = class_to_subsys(class);
-
-	/* two puts are required as the call to bus_to_subsys incremented it again */
-	subsys_put(sp);
-	subsys_put(sp);
-}
-
 static ssize_t class_attr_show(struct kobject *kobj, struct attribute *attr,
 			       char *buf)
 {
@@ -148,13 +130,15 @@ static const struct kobj_type class_ktype = {
 int class_create_file_ns(const struct class *cls, const struct class_attribute *attr,
 			 const void *ns)
 {
+	struct subsys_private *sp = class_to_subsys(cls);
 	int error;
 
-	if (cls)
-		error = sysfs_create_file_ns(&cls->p->subsys.kobj,
-					     &attr->attr, ns);
-	else
-		error = -EINVAL;
+	if (!sp)
+		return -EINVAL;
+
+	error = sysfs_create_file_ns(&sp->subsys.kobj, &attr->attr, ns);
+	subsys_put(sp);
+
 	return error;
 }
 EXPORT_SYMBOL_GPL(class_create_file_ns);
@@ -162,8 +146,13 @@ EXPORT_SYMBOL_GPL(class_create_file_ns);
 void class_remove_file_ns(const struct class *cls, const struct class_attribute *attr,
 			  const void *ns)
 {
-	if (cls)
-		sysfs_remove_file_ns(&cls->p->subsys.kobj, &attr->attr, ns);
+	struct subsys_private *sp = class_to_subsys(cls);
+
+	if (!sp)
+		return;
+
+	sysfs_remove_file_ns(&sp->subsys.kobj, &attr->attr, ns);
+	subsys_put(sp);
 }
 EXPORT_SYMBOL_GPL(class_remove_file_ns);
 
@@ -187,18 +176,6 @@ static void klist_class_dev_put(struct klist_node *n)
 	put_device(dev);
 }
 
-static int class_add_groups(const struct class *cls,
-			    const struct attribute_group **groups)
-{
-	return sysfs_create_groups(&cls->p->subsys.kobj, groups);
-}
-
-static void class_remove_groups(const struct class *cls,
-				const struct attribute_group **groups)
-{
-	return sysfs_remove_groups(&cls->p->subsys.kobj, groups);
-}
-
 int class_register(struct class *cls)
 {
 	struct subsys_private *cp;
@@ -235,8 +212,7 @@ int class_register(struct class *cls)
 	if (error)
 		goto err_out;
 
-	error = class_add_groups(class_get(cls), cls->class_groups);
-	class_put(cls);
+	error = sysfs_create_groups(&cp->subsys.kobj, cls->class_groups);
 	if (error) {
 		kobject_del(&cp->subsys.kobj);
 		kfree_const(cp->subsys.kobj.name);
@@ -253,9 +229,16 @@ EXPORT_SYMBOL_GPL(class_register);
 
 void class_unregister(const struct class *cls)
 {
+	struct subsys_private *sp = class_to_subsys(cls);
+
+	if (!sp)
+		return;
+
 	pr_debug("device class '%s': unregistering\n", cls->name);
-	class_remove_groups(cls, cls->class_groups);
-	kset_unregister(&cls->p->subsys);
+
+	sysfs_remove_groups(&sp->subsys.kobj, cls->class_groups);
+	kset_unregister(&sp->subsys);
+	subsys_put(sp);
 }
 EXPORT_SYMBOL_GPL(class_unregister);
 
@@ -335,11 +318,15 @@ EXPORT_SYMBOL_GPL(class_destroy);
 void class_dev_iter_init(struct class_dev_iter *iter, const struct class *class,
 			 const struct device *start, const struct device_type *type)
 {
+	struct subsys_private *sp = class_to_subsys(class);
 	struct klist_node *start_knode = NULL;
 
+	if (!sp)
+		return;
+
 	if (start)
 		start_knode = &start->p->knode_class;
-	klist_iter_init_node(&class->p->klist_devices, &iter->ki, start_knode);
+	klist_iter_init_node(&sp->klist_devices, &iter->ki, start_knode);
 	iter->type = type;
 }
 EXPORT_SYMBOL_GPL(class_dev_iter_init);
@@ -406,13 +393,14 @@ EXPORT_SYMBOL_GPL(class_dev_iter_exit);
 int class_for_each_device(const struct class *class, const struct device *start,
 			  void *data, int (*fn)(struct device *, void *))
 {
+	struct subsys_private *sp = class_to_subsys(class);
 	struct class_dev_iter iter;
 	struct device *dev;
 	int error = 0;
 
 	if (!class)
 		return -EINVAL;
-	if (!class->p) {
+	if (!sp) {
 		WARN(1, "%s called for class '%s' before it was initialized",
 		     __func__, class->name);
 		return -EINVAL;
@@ -425,6 +413,7 @@ int class_for_each_device(const struct class *class, const struct device *start,
 			break;
 	}
 	class_dev_iter_exit(&iter);
+	subsys_put(sp);
 
 	return error;
 }
@@ -454,12 +443,13 @@ struct device *class_find_device(const struct class *class, const struct device
 				 const void *data,
 				 int (*match)(struct device *, const void *))
 {
+	struct subsys_private *sp = class_to_subsys(class);
 	struct class_dev_iter iter;
 	struct device *dev;
 
 	if (!class)
 		return NULL;
-	if (!class->p) {
+	if (!sp) {
 		WARN(1, "%s called for class '%s' before it was initialized",
 		     __func__, class->name);
 		return NULL;
@@ -473,6 +463,7 @@ struct device *class_find_device(const struct class *class, const struct device
 		}
 	}
 	class_dev_iter_exit(&iter);
+	subsys_put(sp);
 
 	return dev;
 }
@@ -480,6 +471,7 @@ EXPORT_SYMBOL_GPL(class_find_device);
 
 int class_interface_register(struct class_interface *class_intf)
 {
+	struct subsys_private *sp;
 	const struct class *parent;
 	struct class_dev_iter iter;
 	struct device *dev;
@@ -487,19 +479,25 @@ int class_interface_register(struct class_interface *class_intf)
 	if (!class_intf || !class_intf->class)
 		return -ENODEV;
 
-	parent = class_get(class_intf->class);
-	if (!parent)
+	parent = class_intf->class;
+	sp = class_to_subsys(parent);
+	if (!sp)
 		return -EINVAL;
 
-	mutex_lock(&parent->p->mutex);
-	list_add_tail(&class_intf->node, &parent->p->interfaces);
+	/*
+	 * Reference in sp is now incremented and will be dropped when
+	 * the interface is removed in the call to class_interface_unregister()
+	 */
+
+	mutex_lock(&sp->mutex);
+	list_add_tail(&class_intf->node, &sp->interfaces);
 	if (class_intf->add_dev) {
 		class_dev_iter_init(&iter, parent, NULL, NULL);
 		while ((dev = class_dev_iter_next(&iter)))
 			class_intf->add_dev(dev, class_intf);
 		class_dev_iter_exit(&iter);
 	}
-	mutex_unlock(&parent->p->mutex);
+	mutex_unlock(&sp->mutex);
 
 	return 0;
 }
@@ -507,6 +505,7 @@ EXPORT_SYMBOL_GPL(class_interface_register);
 
 void class_interface_unregister(struct class_interface *class_intf)
 {
+	struct subsys_private *sp;
 	struct class *parent = class_intf->class;
 	struct class_dev_iter iter;
 	struct device *dev;
@@ -514,7 +513,11 @@ void class_interface_unregister(struct class_interface *class_intf)
 	if (!parent)
 		return;
 
-	mutex_lock(&parent->p->mutex);
+	sp = class_to_subsys(parent);
+	if (!sp)
+		return;
+
+	mutex_lock(&sp->mutex);
 	list_del_init(&class_intf->node);
 	if (class_intf->remove_dev) {
 		class_dev_iter_init(&iter, parent, NULL, NULL);
@@ -522,9 +525,15 @@ void class_interface_unregister(struct class_interface *class_intf)
 			class_intf->remove_dev(dev, class_intf);
 		class_dev_iter_exit(&iter);
 	}
-	mutex_unlock(&parent->p->mutex);
+	mutex_unlock(&sp->mutex);
 
-	class_put(parent);
+	/*
+	 * Decrement the reference count twice, once for the class_to_subsys()
+	 * call in the start of this function, and the second one from the
+	 * reference increment in class_interface_register()
+	 */
+	subsys_put(sp);
+	subsys_put(sp);
 }
 EXPORT_SYMBOL_GPL(class_interface_unregister);
 
-- 
2.40.0