[PATCH] I2C: Check for unregistered adapter in i2c_del_adapter

The patch adds a check at the beginning of i2c_del_adapter in case
someone attempts to remove an adapter that was never added in the first
place. This sounds like a good safety, as doing so will lead to an oops
at the moment. Also, I have a need for it in the latest version of my
i2c-amd756-s4882 patch. I need to remove the original adapter and
install the virtual ones instead, but I have no way to know if the
original adapter was succesfully added beforehand or not.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/i2c/i2c-core.c

@@ -177,12 +177,25 @@ int i2c_add_adapter(struct i2c_adapter *adap)
 int i2c_del_adapter(struct i2c_adapter *adap)
 {
 	struct list_head  *item, *_n;
+	struct i2c_adapter *adap_from_list;
 	struct i2c_driver *driver;
 	struct i2c_client *client;
 	int res = 0;
 
 	down(&core_lists);
 
+	/* First make sure that this adapter was ever added */
+	list_for_each_entry(adap_from_list, &adapters, list) {
+		if (adap_from_list == adap)
+			break;
+	}
+	if (adap_from_list != adap) {
+		pr_debug("I2C: Attempting to delete an unregistered "
+			 "adapter\n");
+		res = -EINVAL;
+		goto out_unlock;
+	}
+
 	list_for_each(item,&drivers) {
 		driver = list_entry(item, struct i2c_driver, list);
 		if (driver->detach_adapter)