[PATCH v3 1/2] usb: roles: fix NULL pointer issue when put module's reference

[Xu Yang <xu.yang_2@xxxxxxx>]

In current design, usb role class driver will get usb_role_switch parent's
module reference after the user get usb_role_switch device and put the
reference after the user put the usb_role_switch device. However, the
parent device of usb_role_switch may be removed before the user put the
usb_role_switch. If so, then, NULL pointer issue will be met when the user
put the parent module's reference.

This will save the module pointer in structure of usb_role_switch. Then,
we don't need to find module by iterating long relations.

Fixes: 5c54fcac9a9d ("usb: roles: Take care of driver module reference counting")
cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Xu Yang <xu.yang_2@xxxxxxx>

---
Changes in v2:
 - save module pointer as a member of usb_role_switch as suggested by Alan
Changes in v3:
 - no changes
---
 drivers/usb/roles/class.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/roles/class.c b/drivers/usb/roles/class.c
index ae41578bd014..2bad038fb9ad 100644
--- a/drivers/usb/roles/class.c
+++ b/drivers/usb/roles/class.c
@@ -21,6 +21,7 @@ static const struct class role_class = {
 struct usb_role_switch {
 	struct device dev;
 	struct mutex lock; /* device lock*/
+	struct module *module; /* the module this device depends on */
 	enum usb_role role;
 
 	/* From descriptor */
@@ -135,7 +136,7 @@ struct usb_role_switch *usb_role_switch_get(struct device *dev)
 						  usb_role_switch_match);
 
 	if (!IS_ERR_OR_NULL(sw))
-		WARN_ON(!try_module_get(sw->dev.parent->driver->owner));
+		WARN_ON(!try_module_get(sw->module));
 
 	return sw;
 }
@@ -157,7 +158,7 @@ struct usb_role_switch *fwnode_usb_role_switch_get(struct fwnode_handle *fwnode)
 		sw = fwnode_connection_find_match(fwnode, "usb-role-switch",
 						  NULL, usb_role_switch_match);
 	if (!IS_ERR_OR_NULL(sw))
-		WARN_ON(!try_module_get(sw->dev.parent->driver->owner));
+		WARN_ON(!try_module_get(sw->module));
 
 	return sw;
 }
@@ -172,7 +173,7 @@ EXPORT_SYMBOL_GPL(fwnode_usb_role_switch_get);
 void usb_role_switch_put(struct usb_role_switch *sw)
 {
 	if (!IS_ERR_OR_NULL(sw)) {
-		module_put(sw->dev.parent->driver->owner);
+		module_put(sw->module);
 		put_device(&sw->dev);
 	}
 }
@@ -189,15 +190,18 @@ struct usb_role_switch *
 usb_role_switch_find_by_fwnode(const struct fwnode_handle *fwnode)
 {
 	struct device *dev;
+	struct usb_role_switch *sw = NULL;
 
 	if (!fwnode)
 		return NULL;
 
 	dev = class_find_device_by_fwnode(&role_class, fwnode);
-	if (dev)
-		WARN_ON(!try_module_get(dev->parent->driver->owner));
+	if (dev) {
+		sw = to_role_switch(dev);
+		WARN_ON(!try_module_get(sw->module));
+	}
 
-	return dev ? to_role_switch(dev) : NULL;
+	return sw;
 }
 EXPORT_SYMBOL_GPL(usb_role_switch_find_by_fwnode);
 
@@ -338,6 +342,7 @@ usb_role_switch_register(struct device *parent,
 	sw->set = desc->set;
 	sw->get = desc->get;
 
+	sw->module = parent->driver->owner;
 	sw->dev.parent = parent;
 	sw->dev.fwnode = desc->fwnode;
 	sw->dev.class = &role_class;
-- 
2.34.1