target: Fix target_core_register_fabric() for built-in fabric modules

If we try to create a fabric directory in configfs for one of the
default hard-coded fabric modules (iscsi and loopback), and that
fabric is actually built into the kernel, then the operation will
spuriously fail because request_module() (for the code that's already
linked into the kernel) fails.

Fix this by running the autoprobing code only if an initial
target_core_get_fabric() fails.
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_configfs.c

@@ -126,6 +126,12 @@ static struct config_group *target_core_register_fabric(
 
 	pr_debug("Target_Core_ConfigFS: REGISTER -> group: %p name:"
 			" %s\n", group, name);
+
+	tf = target_core_get_fabric(name);
+	if (!tf) {
+		pr_err("target_core_register_fabric() trying autoload for %s\n",
+			name);
+
 		/*
 		 * Below are some hardcoded request_module() calls to automatically
 		 * local fabric modules when the following is called:
@@ -136,6 +142,7 @@ static struct config_group *target_core_register_fabric(
 		 * registered, but simply provids auto loading logic for modules with
 		 * mkdir(2) system calls with known TCM fabric modules.
 		 */
+
 		if (!strncmp(name, "iscsi", 5)) {
 			/*
 			 * Automatically load the LIO Target fabric module when the
@@ -165,6 +172,8 @@ static struct config_group *target_core_register_fabric(
 		}
 
 		tf = target_core_get_fabric(name);
+	}
+
 	if (!tf) {
 		pr_err("target_core_get_fabric() failed for %s\n",
 		       name);