block/rnbd: Remove a useless mutex

According to lib/idr.c,
   The IDA handles its own locking.  It is safe to call any of the IDA
   functions without synchronisation in your code.

so the 'ida_lock' mutex can just be removed.
It is here only to protect some ida_simple_get()/ida_simple_remove() calls.

While at it, switch to ida_alloc_XXX()/ida_free() instead to
ida_simple_get()/ida_simple_remove().
The latter is deprecated and more verbose.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Jack Wang <jinpu.wang@ionos.com>
Link: https://lore.kernel.org/r/7f9eccd8b1fce1bac45ac9b01a78cf72f54c0a61.1644266862.git.christophe.jaillet@wanadoo.frSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/rnbd/rnbd-clt.c

@@ -23,7 +23,6 @@ MODULE_LICENSE("GPL");
 
 static int rnbd_client_major;
 static DEFINE_IDA(index_ida);
-static DEFINE_MUTEX(ida_lock);
 static DEFINE_MUTEX(sess_lock);
 static LIST_HEAD(sess_list);
 
@@ -55,9 +54,7 @@ static void rnbd_clt_put_dev(struct rnbd_clt_dev *dev)
 	if (!refcount_dec_and_test(&dev->refcount))
 		return;
 
-	mutex_lock(&ida_lock);
-	ida_simple_remove(&index_ida, dev->clt_device_id);
-	mutex_unlock(&ida_lock);
+	ida_free(&index_ida, dev->clt_device_id);
 	kfree(dev->hw_queues);
 	kfree(dev->pathname);
 	rnbd_clt_put_sess(dev->sess);
@@ -1460,10 +1457,8 @@ static struct rnbd_clt_dev *init_dev(struct rnbd_clt_session *sess,
 		goto out_alloc;
 	}
 
-	mutex_lock(&ida_lock);
-	ret = ida_simple_get(&index_ida, 0, 1 << (MINORBITS - RNBD_PART_BITS),
+	ret = ida_alloc_max(&index_ida, 1 << (MINORBITS - RNBD_PART_BITS),
 			    GFP_KERNEL);
-	mutex_unlock(&ida_lock);
 	if (ret < 0) {
 		pr_err("Failed to initialize device '%s' from session %s, allocating idr failed, err: %d\n",
 		       pathname, sess->sessname, ret);