i2c: Use a separate mutex for userspace client lists

Moving userspace-instantiated clients to separate lists wasn't nearly
enough to avoid deadlocks in multiplexed bus cases. We also want to
have a dedicated mutex to protect each list.

Signed-off-by: Jean Delvare <[e-mail]>
Cc: Michael Lawnick <[e-mail]>

drivers/i2c/i2c-core.c

···
 		return -EINVAL;
 
 	/* Keep track of the added device */
-	i2c_lock_adapter(adap);
+	mutex_lock(&adap->userspace_clients_lock);
 	list_add_tail(&client->detected, &adap->userspace_clients);
-	i2c_unlock_adapter(adap);
+	mutex_unlock(&adap->userspace_clients_lock);
 	dev_info(dev, "%s: Instantiated device %s at 0x%02hx\n", "new_device",
 		 info.type, info.addr);
 
···
 
 	/* Make sure the device was added through sysfs */
 	res = -ENOENT;
-	i2c_lock_adapter(adap);
+	mutex_lock(&adap->userspace_clients_lock);
 	list_for_each_entry_safe(client, next, &adap->userspace_clients,
 				 detected) {
 		if (client->addr == addr) {
···
 			break;
 		}
 	}
-	i2c_unlock_adapter(adap);
+	mutex_unlock(&adap->userspace_clients_lock);
 
 	if (res < 0)
 		dev_err(dev, "%s: Can't find device in list\n",
···
 	}
 
 	rt_mutex_init(&adap->bus_lock);
+	mutex_init(&adap->userspace_clients_lock);
 	INIT_LIST_HEAD(&adap->userspace_clients);
 
 	/* Set default timeout to 1 second if not already set */
···
 		return res;
 
 	/* Remove devices instantiated from sysfs */
-	i2c_lock_adapter(adap);
+	mutex_lock(&adap->userspace_clients_lock);
 	list_for_each_entry_safe(client, next, &adap->userspace_clients,
 				 detected) {
 		dev_dbg(&adap->dev, "Removing %s at 0x%x\n", client->name,
···
 		list_del(&client->detected);
 		i2c_unregister_device(client);
 	}
-	i2c_unlock_adapter(adap);
+	mutex_unlock(&adap->userspace_clients_lock);
 
 	/* Detach any active clients. This can't fail, thus we do not
 	   checking the returned value. */

include/linux/i2c.h

···
 	char name[48];
 	struct completion dev_released;
 
+	struct mutex userspace_clients_lock;
 	struct list_head userspace_clients;
 };
 #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)