iscsi-target: Convert to use target_put_session + sess_kref

This patch converts iscsi-target session code to use se_sess->sess_kref
counting for iscsi session shutdown.  The following cases include:

*) last iscsit_close_connection() shutdown path to invoke close session
*) iscsit_logout_post_handler_closesession() for explict logout
*) iscsit_free_session() caller for explict shutdown

It also moves iscsit_stop_session() call from lio_tpg_close_session()
into lio_tpg_shutdown_session() TFO callbacks to invoke an explict
shutdown, and also changes iscsi_check_for_session_reinstatement()
login code to use se_sess->sess_kref.

(v2: Make iscsit_handle_time2retain_timeout() use target_put_session)

Cc: Andy Grover <agrover@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target.c

@@ -4168,7 +4168,7 @@ int iscsit_close_connection(
 	if (!atomic_read(&sess->session_reinstatement) &&
 	     atomic_read(&sess->session_fall_back_to_erl0)) {
 		spin_unlock_bh(&sess->conn_lock);
-		iscsit_close_session(sess);
+		target_put_session(sess->se_sess);
 
 		return 0;
 	} else if (atomic_read(&sess->session_logout)) {
@@ -4289,7 +4289,7 @@ static void iscsit_logout_post_handler_closesession(
 	iscsit_dec_conn_usage_count(conn);
 	iscsit_stop_session(sess, 1, 1);
 	iscsit_dec_session_usage_count(sess);
-	iscsit_close_session(sess);
+	target_put_session(sess->se_sess);
 }
 
 static void iscsit_logout_post_handler_samecid(
@@ -4455,7 +4455,7 @@ int iscsit_free_session(struct iscsi_session *sess)
 	} else
 		spin_unlock_bh(&sess->conn_lock);
 
-	iscsit_close_session(sess);
+	target_put_session(sess->se_sess);
 	return 0;
 }
 

drivers/target/iscsi/iscsi_target_configfs.c

@@ -1698,8 +1698,8 @@ static int lio_tpg_shutdown_session(struct se_session *se_sess)
 	atomic_set(&sess->session_reinstatement, 1);
 	spin_unlock(&sess->conn_lock);
 
-	iscsit_inc_session_usage_count(sess);
 	iscsit_stop_time2retain_timer(sess);
+	iscsit_stop_session(sess, 1, 1);
 
 	return 1;
 }
@@ -1715,8 +1715,6 @@ static void lio_tpg_close_session(struct se_session *se_sess)
 	 * If the iSCSI Session for the iSCSI Initiator Node exists,
 	 * forcefully shutdown the iSCSI NEXUS.
 	 */
-	iscsit_stop_session(sess, 1, 1);
-	iscsit_dec_session_usage_count(sess);
 	iscsit_close_session(sess);
 }
 

drivers/target/iscsi/iscsi_target_erl0.c

@@ -783,7 +783,7 @@ static void iscsit_handle_time2retain_timeout(unsigned long data)
 	}
 
 	spin_unlock_bh(&se_tpg->session_lock);
-	iscsit_close_session(sess);
+	target_put_session(sess->se_sess);
 }
 
 extern void iscsit_start_time2retain_handler(struct iscsi_session *sess)

drivers/target/iscsi/iscsi_target_login.c

@@ -180,14 +180,16 @@ int iscsi_check_for_session_reinstatement(struct iscsi_conn *conn)
 	if (sess->session_state == TARG_SESS_STATE_FAILED) {
 		spin_unlock_bh(&sess->conn_lock);
 		iscsit_dec_session_usage_count(sess);
-		return iscsit_close_session(sess);
+		target_put_session(sess->se_sess);
+		return 0;
 	}
 	spin_unlock_bh(&sess->conn_lock);
 
 	iscsit_stop_session(sess, 1, 1);
 	iscsit_dec_session_usage_count(sess);
 
-	return iscsit_close_session(sess);
+	target_put_session(sess->se_sess);
+	return 0;
 }
 
 static void iscsi_login_set_conn_values(