iscsi-target: Fix iser explicit logout TX kthread leak

This patch fixes a regression introduced with the following commit
in v4.0-rc1 code, where an explicit iser-target logout would result
in ->tx_thread_active being incorrectly cleared by the logout post
handler, and subsequent TX kthread leak:

commit 88dcd2dab5c23b1c9cfc396246d8f476c872f0ca
Author: Nicholas Bellinger <[e-mail]>
Date: Thu Feb 26 22:19:15 2015 -0800

iscsi-target: Convert iscsi_thread_set usage to kthread.h

To address this bug, change iscsit_logout_post_handler_closesession()
and iscsit_logout_post_handler_samecid() to only cmpxchg() on
->tx_thread_active for traditional iscsi/tcp connections.

This is required because iscsi/tcp connections are invoking logout
post handler logic directly from TX kthread context, while iser
connections are invoking logout post handler logic from a seperate
workqueue context.

Cc: Sagi Grimberg <[e-mail]>
Cc: <[e-mail]> # v3.10+
Signed-off-by: Nicholas Bellinger <[e-mail]>

drivers/target/iscsi/iscsi_target.c

···
 	struct iscsi_conn *conn)
 {
 	struct iscsi_session *sess = conn->sess;
-	int sleep = cmpxchg(&conn->tx_thread_active, true, false);
+	int sleep = 1;
+	/*
+	 * Traditional iscsi/tcp will invoke this logic from TX thread
+	 * context during session logout, so clear tx_thread_active and
+	 * sleep if iscsit_close_connection() has not already occured.
+	 *
+	 * Since iser-target invokes this logic from it's own workqueue,
+	 * always sleep waiting for RX/TX thread shutdown to complete
+	 * within iscsit_close_connection().
+	 */
+	if (conn->conn_transport->transport_type == ISCSI_TCP)
+		sleep = cmpxchg(&conn->tx_thread_active, true, false);
 
 	atomic_set(&conn->conn_logout_remove, 0);
 	complete(&conn->conn_logout_comp);
···
 static void iscsit_logout_post_handler_samecid(
 	struct iscsi_conn *conn)
 {
-	int sleep = cmpxchg(&conn->tx_thread_active, true, false);
+	int sleep = 1;
+
+	if (conn->conn_transport->transport_type == ISCSI_TCP)
+		sleep = cmpxchg(&conn->tx_thread_active, true, false);
 
 	atomic_set(&conn->conn_logout_remove, 0);
 	complete(&conn->conn_logout_comp);