Date:	Sun, 6 Mar 2016 23:26:29 +0530
From:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] parport: register driver later

On Sat, Mar 05, 2016 at 12:19:32PM -0800, Greg KH wrote:
> On Fri, Mar 04, 2016 at 04:20:59PM +0530, Sudip Mukherjee wrote:
> > If the parport bus is not yet registered and any device using parallel
> > port tries to register with the bus we get a stackdump with a message
> > of Kernel bug.
> > 
> > Reported-by: Fengguang Wu <fengguang.wu@...el.com>
> > Tested-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> > Cc: <stable@...r.kernel.org> # 4.2+ 
> > Signed-off-by: Sudip Mukherjee <sudip.mukherjee@...ethink.co.uk>
> > ---
> > 
> > We should actually have some deferred probe here. But considering that
> > you will be closing your trees soon so a quick fix to solve the problem
> > for now. We will revisit this when we remove the old api (hopefully v4.7).
> > 
> >  drivers/parport/share.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/parport/share.c b/drivers/parport/share.c
> > index 3308427..176b2b6 100644
> > --- a/drivers/parport/share.c
> > +++ b/drivers/parport/share.c
> > @@ -273,6 +273,9 @@ int __parport_register_driver(struct parport_driver *drv, struct module *owner,
> >  		/* using device model */
> >  		int ret;
> >  
> > +		if (!parport_bus_type.p)
> > +			return -EAGAIN;
> 
> I really don't like it when busses poke into the driver-core
> internal-only structures like this.  Why can't you have your own "have
> been registered" flag instead if you really need it?  Don't rely on the
> driver core here to be doing this always this way, perhaps p could be
> NULL and it only is created later on somehow?

I saw that in i2c and spmi and followed. Sent you v2 for your review. I
will send a patch to remove the use of 'p' in those places.

> 
> I need to rename 'p' to "do_not_touch_you_have_been_warned" or something
> else...

something like this (compile tested) ?
(do you want me to send a proper patch?):

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 6470eb8..4fa350e 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -40,7 +40,7 @@ static int __must_check bus_rescan_devices_helper(struct device *dev,
 static struct bus_type *bus_get(struct bus_type *bus)
 {
 	if (bus) {
-		kset_get(&bus->p->subsys);
+		kset_get(&bus->do_not_touch_u_r_warned->subsys);
 		return bus;
 	}
 	return NULL;
@@ -49,7 +49,7 @@ static struct bus_type *bus_get(struct bus_type *bus)
 static void bus_put(struct bus_type *bus)
 {
 	if (bus)
-		kset_put(&bus->p->subsys);
+		kset_put(&bus->do_not_touch_u_r_warned->subsys);
 }
 
 static ssize_t drv_attr_show(struct kobject *kobj, struct attribute *attr,
@@ -130,7 +130,9 @@ int bus_create_file(struct bus_type *bus, struct bus_attribute *attr)
 {
 	int error;
 	if (bus_get(bus)) {
-		error = sysfs_create_file(&bus->p->subsys.kobj, &attr->attr);
+		error = sysfs_create_file(&bus->
+					  do_not_touch_u_r_warned->
+					  subsys.kobj, &attr->attr);
 		bus_put(bus);
 	} else
 		error = -EINVAL;
@@ -141,7 +143,8 @@ EXPORT_SYMBOL_GPL(bus_create_file);
 void bus_remove_file(struct bus_type *bus, struct bus_attribute *attr)
 {
 	if (bus_get(bus)) {
-		sysfs_remove_file(&bus->p->subsys.kobj, &attr->attr);
+		sysfs_remove_file(&bus->do_not_touch_u_r_warned->
+				  subsys.kobj, &attr->attr);
 		bus_put(bus);
 	}
 }
@@ -153,7 +156,7 @@ static void bus_release(struct kobject *kobj)
 	struct bus_type *bus = priv->bus;
 
 	kfree(priv);
-	bus->p = NULL;
+	bus->do_not_touch_u_r_warned = NULL;
 }
 
 static struct kobj_type bus_ktype = {
@@ -237,16 +240,17 @@ static DRIVER_ATTR_WO(bind);
 
 static ssize_t show_drivers_autoprobe(struct bus_type *bus, char *buf)
 {
-	return sprintf(buf, "%d\n", bus->p->drivers_autoprobe);
+	return sprintf(buf, "%d\n",
+		       bus->do_not_touch_u_r_warned->drivers_autoprobe);
 }
 
 static ssize_t store_drivers_autoprobe(struct bus_type *bus,
 				       const char *buf, size_t count)
 {
 	if (buf[0] == '0')
-		bus->p->drivers_autoprobe = 0;
+		bus->do_not_touch_u_r_warned->drivers_autoprobe = 0;
 	else
-		bus->p->drivers_autoprobe = 1;
+		bus->do_not_touch_u_r_warned->drivers_autoprobe = 1;
 	return count;
 }
 
@@ -304,10 +308,10 @@ int bus_for_each_dev(struct bus_type *bus, struct device *start,
 	struct device *dev;
 	int error = 0;
 
-	if (!bus || !bus->p)
+	if (!bus || !bus->do_not_touch_u_r_warned)
 		return -EINVAL;
 
-	klist_iter_init_node(&bus->p->klist_devices, &i,
+	klist_iter_init_node(&bus->do_not_touch_u_r_warned->klist_devices, &i,
 			     (start ? &start->p->knode_bus : NULL));
 	while ((dev = next_device(&i)) && !error)
 		error = fn(dev, data);
@@ -338,10 +342,11 @@ struct device *bus_find_device(struct bus_type *bus,
 	struct klist_iter i;
 	struct device *dev;
 
-	if (!bus || !bus->p)
+	if (!bus || !bus->do_not_touch_u_r_warned)
 		return NULL;
 
-	klist_iter_init_node(&bus->p->klist_devices, &i,
+	klist_iter_init_node(&bus->do_not_touch_u_r_warned->
+			     klist_devices, &i,
 			     (start ? &start->p->knode_bus : NULL));
 	while ((dev = next_device(&i)))
 		if (match(dev, data) && get_device(dev))
@@ -395,7 +400,9 @@ struct device *subsys_find_device_by_id(struct bus_type *subsys, unsigned int id
 		return NULL;
 
 	if (hint) {
-		klist_iter_init_node(&subsys->p->klist_devices, &i, &hint->p->knode_bus);
+		klist_iter_init_node(&subsys->do_not_touch_u_r_warned->
+				     klist_devices, &i,
+				     &hint->p->knode_bus);
 		dev = next_device(&i);
 		if (dev && dev->id == id && get_device(dev)) {
 			klist_iter_exit(&i);
@@ -404,7 +411,8 @@ struct device *subsys_find_device_by_id(struct bus_type *subsys, unsigned int id
 		klist_iter_exit(&i);
 	}
 
-	klist_iter_init_node(&subsys->p->klist_devices, &i, NULL);
+	klist_iter_init_node(&subsys->do_not_touch_u_r_warned->
+			     klist_devices, &i, NULL);
 	while ((dev = next_device(&i))) {
 		if (dev->id == id && get_device(dev)) {
 			klist_iter_exit(&i);
@@ -457,8 +465,8 @@ int bus_for_each_drv(struct bus_type *bus, struct device_driver *start,
 	if (!bus)
 		return -EINVAL;
 
-	klist_iter_init_node(&bus->p->klist_drivers, &i,
-			     start ? &start->p->knode_bus : NULL);
+	klist_iter_init_node(&bus->do_not_touch_u_r_warned->klist_drivers,
+			     &i, start ? &start->p->knode_bus : NULL);
 	while ((drv = next_driver(&i)) && !error)
 		error = fn(drv, data);
 	klist_iter_exit(&i);
@@ -516,20 +524,24 @@ int bus_add_device(struct device *dev)
 		error = device_add_groups(dev, bus->dev_groups);
 		if (error)
 			goto out_id;
-		error = sysfs_create_link(&bus->p->devices_kset->kobj,
-						&dev->kobj, dev_name(dev));
+		error = sysfs_create_link(&bus->do_not_touch_u_r_warned->
+					  devices_kset->kobj, &dev->kobj,
+					  dev_name(dev));
 		if (error)
 			goto out_groups;
 		error = sysfs_create_link(&dev->kobj,
-				&dev->bus->p->subsys.kobj, "subsystem");
+					  &dev->bus->do_not_touch_u_r_warned->
+					  subsys.kobj, "subsystem");
 		if (error)
 			goto out_subsys;
-		klist_add_tail(&dev->p->knode_bus, &bus->p->klist_devices);
+		klist_add_tail(&dev->p->knode_bus,
+			       &bus->do_not_touch_u_r_warned->klist_devices);
 	}
 	return 0;
 
 out_subsys:
-	sysfs_remove_link(&bus->p->devices_kset->kobj, dev_name(dev));
+	sysfs_remove_link(&bus->do_not_touch_u_r_warned->devices_kset->kobj,
+			  dev_name(dev));
 out_groups:
 	device_remove_groups(dev, bus->dev_groups);
 out_id:
@@ -553,14 +565,15 @@ void bus_probe_device(struct device *dev)
 	if (!bus)
 		return;
 
-	if (bus->p->drivers_autoprobe)
+	if (bus->do_not_touch_u_r_warned->drivers_autoprobe)
 		device_initial_probe(dev);
 
-	mutex_lock(&bus->p->mutex);
-	list_for_each_entry(sif, &bus->p->interfaces, node)
+	mutex_lock(&bus->do_not_touch_u_r_warned->mutex);
+	list_for_each_entry(sif, &bus->do_not_touch_u_r_warned->interfaces,
+			    node)
 		if (sif->add_dev)
 			sif->add_dev(dev, sif);
-	mutex_unlock(&bus->p->mutex);
+	mutex_unlock(&bus->do_not_touch_u_r_warned->mutex);
 }
 
 /**
@@ -581,14 +594,15 @@ void bus_remove_device(struct device *dev)
 	if (!bus)
 		return;
 
-	mutex_lock(&bus->p->mutex);
-	list_for_each_entry(sif, &bus->p->interfaces, node)
+	mutex_lock(&bus->do_not_touch_u_r_warned->mutex);
+	list_for_each_entry(sif, &bus->do_not_touch_u_r_warned->interfaces,
+			    node)
 		if (sif->remove_dev)
 			sif->remove_dev(dev, sif);
-	mutex_unlock(&bus->p->mutex);
+	mutex_unlock(&bus->do_not_touch_u_r_warned->mutex);
 
 	sysfs_remove_link(&dev->kobj, "subsystem");
-	sysfs_remove_link(&dev->bus->p->devices_kset->kobj,
+	sysfs_remove_link(&dev->bus->do_not_touch_u_r_warned->devices_kset->kobj,
 			  dev_name(dev));
 	device_remove_attrs(dev->bus, dev);
 	device_remove_groups(dev, dev->bus->dev_groups);
@@ -691,14 +705,15 @@ int bus_add_driver(struct device_driver *drv)
 	klist_init(&priv->klist_devices, NULL, NULL);
 	priv->driver = drv;
 	drv->p = priv;
-	priv->kobj.kset = bus->p->drivers_kset;
+	priv->kobj.kset = bus->do_not_touch_u_r_warned->drivers_kset;
 	error = kobject_init_and_add(&priv->kobj, &driver_ktype, NULL,
 				     "%s", drv->name);
 	if (error)
 		goto out_unregister;
 
-	klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
-	if (drv->bus->p->drivers_autoprobe) {
+	klist_add_tail(&priv->knode_bus,
+		       &bus->do_not_touch_u_r_warned->klist_drivers);
+	if (drv->bus->do_not_touch_u_r_warned->drivers_autoprobe) {
 		if (driver_allows_async_probing(drv)) {
 			pr_debug("bus: '%s': probing driver %s asynchronously\n",
 				drv->bus->name, drv->name);
@@ -840,13 +855,15 @@ struct bus_type *find_bus(char *name)
 static int bus_add_groups(struct bus_type *bus,
 			  const struct attribute_group **groups)
 {
-	return sysfs_create_groups(&bus->p->subsys.kobj, groups);
+	return sysfs_create_groups(&bus->do_not_touch_u_r_warned->subsys.kobj,
+				   groups);
 }
 
 static void bus_remove_groups(struct bus_type *bus,
 			      const struct attribute_group **groups)
 {
-	sysfs_remove_groups(&bus->p->subsys.kobj, groups);
+	sysfs_remove_groups(&bus->do_not_touch_u_r_warned->subsys.kobj,
+			    groups);
 }
 
 static void klist_devices_get(struct klist_node *n)
@@ -871,7 +888,8 @@ static ssize_t bus_uevent_store(struct bus_type *bus,
 	enum kobject_action action;
 
 	if (kobject_action_type(buf, count, &action) == 0)
-		kobject_uevent(&bus->p->subsys.kobj, action);
+		kobject_uevent(&bus->do_not_touch_u_r_warned->subsys.kobj,
+			       action);
 	return count;
 }
 static BUS_ATTR(uevent, S_IWUSR, NULL, bus_uevent_store);
@@ -895,7 +913,7 @@ int bus_register(struct bus_type *bus)
 		return -ENOMEM;
 
 	priv->bus = bus;
-	bus->p = priv;
+	bus->do_not_touch_u_r_warned = priv;
 
 	BLOCKING_INIT_NOTIFIER_HEAD(&priv->bus_notifier);
 
@@ -948,16 +966,16 @@ int bus_register(struct bus_type *bus)
 bus_groups_fail:
 	remove_probe_files(bus);
 bus_probe_files_fail:
-	kset_unregister(bus->p->drivers_kset);
+	kset_unregister(bus->do_not_touch_u_r_warned->drivers_kset);
 bus_drivers_fail:
-	kset_unregister(bus->p->devices_kset);
+	kset_unregister(bus->do_not_touch_u_r_warned->devices_kset);
 bus_devices_fail:
 	bus_remove_file(bus, &bus_attr_uevent);
 bus_uevent_fail:
-	kset_unregister(&bus->p->subsys);
+	kset_unregister(&bus->do_not_touch_u_r_warned->subsys);
 out:
-	kfree(bus->p);
-	bus->p = NULL;
+	kfree(bus->do_not_touch_u_r_warned);
+	bus->do_not_touch_u_r_warned = NULL;
 	return retval;
 }
 EXPORT_SYMBOL_GPL(bus_register);
@@ -976,34 +994,37 @@ void bus_unregister(struct bus_type *bus)
 		device_unregister(bus->dev_root);
 	bus_remove_groups(bus, bus->bus_groups);
 	remove_probe_files(bus);
-	kset_unregister(bus->p->drivers_kset);
-	kset_unregister(bus->p->devices_kset);
+	kset_unregister(bus->do_not_touch_u_r_warned->drivers_kset);
+	kset_unregister(bus->do_not_touch_u_r_warned->devices_kset);
 	bus_remove_file(bus, &bus_attr_uevent);
-	kset_unregister(&bus->p->subsys);
+	kset_unregister(&bus->do_not_touch_u_r_warned->subsys);
 }
 EXPORT_SYMBOL_GPL(bus_unregister);
 
 int bus_register_notifier(struct bus_type *bus, struct notifier_block *nb)
 {
-	return blocking_notifier_chain_register(&bus->p->bus_notifier, nb);
+	return blocking_notifier_chain_register(&bus->do_not_touch_u_r_warned->
+						bus_notifier, nb);
 }
 EXPORT_SYMBOL_GPL(bus_register_notifier);
 
 int bus_unregister_notifier(struct bus_type *bus, struct notifier_block *nb)
 {
-	return blocking_notifier_chain_unregister(&bus->p->bus_notifier, nb);
+	return blocking_notifier_chain_unregister(&bus->
+						  do_not_touch_u_r_warned->
+						  bus_notifier, nb);
 }
 EXPORT_SYMBOL_GPL(bus_unregister_notifier);
 
 struct kset *bus_get_kset(struct bus_type *bus)
 {
-	return &bus->p->subsys;
+	return &bus->do_not_touch_u_r_warned->subsys;
 }
 EXPORT_SYMBOL_GPL(bus_get_kset);
 
 struct klist *bus_get_device_klist(struct bus_type *bus)
 {
-	return &bus->p->klist_devices;
+	return &bus->do_not_touch_u_r_warned->klist_devices;
 }
 EXPORT_SYMBOL_GPL(bus_get_device_klist);
 
@@ -1076,7 +1097,8 @@ void subsys_dev_iter_init(struct subsys_dev_iter *iter, struct bus_type *subsys,
 
 	if (start)
 		start_knode = &start->p->knode_bus;
-	klist_iter_init_node(&subsys->p->klist_devices, &iter->ki, start_knode);
+	klist_iter_init_node(&subsys->do_not_touch_u_r_warned->klist_devices,
+			     &iter->ki, start_knode);
 	iter->type = type;
 }
 EXPORT_SYMBOL_GPL(subsys_dev_iter_init);
@@ -1135,15 +1157,16 @@ int subsys_interface_register(struct subsys_interface *sif)
 	if (!subsys)
 		return -EINVAL;
 
-	mutex_lock(&subsys->p->mutex);
-	list_add_tail(&sif->node, &subsys->p->interfaces);
+	mutex_lock(&subsys->do_not_touch_u_r_warned->mutex);
+	list_add_tail(&sif->node,
+		      &subsys->do_not_touch_u_r_warned->interfaces);
 	if (sif->add_dev) {
 		subsys_dev_iter_init(&iter, subsys, NULL, NULL);
 		while ((dev = subsys_dev_iter_next(&iter)))
 			sif->add_dev(dev, sif);
 		subsys_dev_iter_exit(&iter);
 	}
-	mutex_unlock(&subsys->p->mutex);
+	mutex_unlock(&subsys->do_not_touch_u_r_warned->mutex);
 
 	return 0;
 }
@@ -1160,7 +1183,7 @@ void subsys_interface_unregister(struct subsys_interface *sif)
 
 	subsys = sif->subsys;
 
-	mutex_lock(&subsys->p->mutex);
+	mutex_lock(&subsys->do_not_touch_u_r_warned->mutex);
 	list_del_init(&sif->node);
 	if (sif->remove_dev) {
 		subsys_dev_iter_init(&iter, subsys, NULL, NULL);
@@ -1168,7 +1191,7 @@ void subsys_interface_unregister(struct subsys_interface *sif)
 			sif->remove_dev(dev, sif);
 		subsys_dev_iter_exit(&iter);
 	}
-	mutex_unlock(&subsys->p->mutex);
+	mutex_unlock(&subsys->do_not_touch_u_r_warned->mutex);
 
 	bus_put(subsys);
 }
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 0a8bdad..c64c746 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1113,7 +1113,9 @@ int device_add(struct device *dev)
 	 * after dpm_sysfs_add() and before kobject_uevent().
 	 */
 	if (dev->bus)
-		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
+		blocking_notifier_call_chain(&dev->bus->
+					     do_not_touch_u_r_warned->
+					     bus_notifier,
 					     BUS_NOTIFY_ADD_DEVICE, dev);
 
 	kobject_uevent(&dev->kobj, KOBJ_ADD);
@@ -1238,7 +1240,9 @@ void device_del(struct device *dev)
 	 * before dpm_sysfs_remove().
 	 */
 	if (dev->bus)
-		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
+		blocking_notifier_call_chain(&dev->bus->
+					     do_not_touch_u_r_warned->
+					     bus_notifier,
 					     BUS_NOTIFY_DEL_DEVICE, dev);
 	dpm_sysfs_remove(dev);
 	if (parent)
@@ -1273,7 +1277,9 @@ void device_del(struct device *dev)
 	if (platform_notify_remove)
 		platform_notify_remove(dev);
 	if (dev->bus)
-		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
+		blocking_notifier_call_chain(&dev->bus->
+					     do_not_touch_u_r_warned->
+					     bus_notifier,
 					     BUS_NOTIFY_REMOVED_DEVICE, dev);
 	kobject_uevent(&dev->kobj, KOBJ_REMOVE);
 	cleanup_device_parent(dev);
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 16688f5..43baef6 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -260,7 +260,9 @@ static void driver_bound(struct device *dev)
 	driver_deferred_probe_trigger();
 
 	if (dev->bus)
-		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
+		blocking_notifier_call_chain(&dev->bus->
+					     do_not_touch_u_r_warned->
+					     bus_notifier,
 					     BUS_NOTIFY_BOUND_DRIVER, dev);
 }
 
@@ -269,7 +271,9 @@ static int driver_sysfs_add(struct device *dev)
 	int ret;
 
 	if (dev->bus)
-		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
+		blocking_notifier_call_chain(&dev->bus->
+					     do_not_touch_u_r_warned->
+					     bus_notifier,
 					     BUS_NOTIFY_BIND_DRIVER, dev);
 
 	ret = sysfs_create_link(&dev->driver->p->kobj, &dev->kobj,
@@ -316,7 +320,9 @@ int device_bind_driver(struct device *dev)
 	if (!ret)
 		driver_bound(dev);
 	else if (dev->bus)
-		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
+		blocking_notifier_call_chain(&dev->bus->
+					     do_not_touch_u_r_warned->
+					     bus_notifier,
 					     BUS_NOTIFY_DRIVER_NOT_BOUND, dev);
 	return ret;
 }
@@ -396,7 +402,9 @@ static int really_probe(struct device *dev, struct device_driver *drv)
 
 probe_failed:
 	if (dev->bus)
-		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
+		blocking_notifier_call_chain(&dev->bus->
+					     do_not_touch_u_r_warned->
+					     bus_notifier,
 					     BUS_NOTIFY_DRIVER_NOT_BOUND, dev);
 pinctrl_bind_failed:
 	devres_release_all(dev);
@@ -770,7 +778,9 @@ static void __device_release_driver(struct device *dev)
 		driver_sysfs_remove(dev);
 
 		if (dev->bus)
-			blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
+			blocking_notifier_call_chain(&dev->bus->
+						     do_not_touch_u_r_warned->
+						     bus_notifier,
 						     BUS_NOTIFY_UNBIND_DRIVER,
 						     dev);
 
@@ -790,7 +800,9 @@ static void __device_release_driver(struct device *dev)
 		klist_remove(&dev->p->knode_driver);
 		device_pm_check_callbacks(dev);
 		if (dev->bus)
-			blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
+			blocking_notifier_call_chain(&dev->bus->
+						     do_not_touch_u_r_warned->
+						     bus_notifier,
 						     BUS_NOTIFY_UNBOUND_DRIVER,
 						     dev);
 	}
diff --git a/drivers/base/driver.c b/drivers/base/driver.c
index 4eabfe2..b8aa7cc 100644
--- a/drivers/base/driver.c
+++ b/drivers/base/driver.c
@@ -150,7 +150,7 @@ int driver_register(struct device_driver *drv)
 	int ret;
 	struct device_driver *other;
 
-	BUG_ON(!drv->bus->p);
+	BUG_ON(!drv->bus->do_not_touch_u_r_warned);
 
 	if ((drv->bus->probe && drv->probe) ||
 	    (drv->bus->remove && drv->remove) ||
@@ -210,7 +210,8 @@ EXPORT_SYMBOL_GPL(driver_unregister);
  */
 struct device_driver *driver_find(const char *name, struct bus_type *bus)
 {
-	struct kobject *k = kset_find_obj(bus->p->drivers_kset, name);
+	struct kobject *k = kset_find_obj(bus->do_not_touch_u_r_warned->
+					  drivers_kset, name);
 	struct driver_private *priv;
 
 	if (k) {
diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index f437afa..cbfd005 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -689,12 +689,14 @@ int __init_or_module __platform_driver_probe(struct platform_driver *drv,
 	 * if the probe was successful, and make sure any forced probes of
 	 * new devices fail.
 	 */
-	spin_lock(&drv->driver.bus->p->klist_drivers.k_lock);
+	spin_lock(&drv->driver.bus->do_not_touch_u_r_warned->
+		  klist_drivers.k_lock);
 	drv->probe = NULL;
 	if (code == 0 && list_empty(&drv->driver.p->klist_devices.k_list))
 		retval = -ENODEV;
 	drv->driver.probe = platform_drv_probe_fail;
-	spin_unlock(&drv->driver.bus->p->klist_drivers.k_lock);
+	spin_unlock(&drv->driver.bus->do_not_touch_u_r_warned->
+		    klist_drivers.k_lock);
 
 	if (code != retval)
 		platform_driver_unregister(drv);
diff --git a/include/linux/device.h b/include/linux/device.h
index 002c597..fb73e9d 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -130,7 +130,7 @@ struct bus_type {
 
 	const struct iommu_ops *iommu_ops;
 
-	struct subsys_private *p;
+	struct subsys_private *do_not_touch_u_r_warned;
 	struct lock_class_key lock_key;
 };
 

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