iscsi-target: Always wait for kthread_should_stop() before kthread exit

There are three timing problems in the kthread usages of iscsi_target_mod:

 - np_thread of struct iscsi_np
 - rx_thread and tx_thread of struct iscsi_conn

In iscsit_close_connection(), it calls

 send_sig(SIGINT, conn->tx_thread, 1);
 kthread_stop(conn->tx_thread);

In conn->tx_thread, which is iscsi_target_tx_thread(), when it receive
SIGINT the kthread will exit without checking the return value of
kthread_should_stop().

So if iscsi_target_tx_thread() exit right between send_sig(SIGINT...)
and kthread_stop(...), the kthread_stop() will try to stop an already
stopped kthread.

This is invalid according to the documentation of kthread_stop().

(Fix -ECONNRESET logout handling in iscsi_target_tx_thread and
 early iscsi_target_rx_thread failure case - nab)

Signed-off-by: Jiang Yi <jiangyilism@gmail.com>
Cc: <stable@vger.kernel.org> # v3.12+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target.c

@@ -3790,6 +3790,8 @@ int iscsi_target_tx_thread(void *arg)
 {
 	int ret = 0;
 	struct iscsi_conn *conn = arg;
+	bool conn_freed = false;
+
 	/*
 	 * Allow ourselves to be interrupted by SIGINT so that a
 	 * connection recovery / failure event can be triggered externally.
@@ -3815,12 +3817,14 @@ int iscsi_target_tx_thread(void *arg)
 			goto transport_err;
 
 		ret = iscsit_handle_response_queue(conn);
-		if (ret == 1)
+		if (ret == 1) {
 			goto get_immediate;
-		else if (ret == -ECONNRESET)
+		} else if (ret == -ECONNRESET) {
+			conn_freed = true;
 			goto out;
-		else if (ret < 0)
+		} else if (ret < 0) {
 			goto transport_err;
+		}
 	}
 
 transport_err:
@@ -3830,8 +3834,13 @@ int iscsi_target_tx_thread(void *arg)
 	 * responsible for cleaning up the early connection failure.
 	 */
 	if (conn->conn_state != TARG_CONN_STATE_IN_LOGIN)
-		iscsit_take_action_for_connection_exit(conn);
+		iscsit_take_action_for_connection_exit(conn, &conn_freed);
 out:
+	if (!conn_freed) {
+		while (!kthread_should_stop()) {
+			msleep(100);
+		}
+	}
 	return 0;
 }
 
@@ -4004,6 +4013,7 @@ int iscsi_target_rx_thread(void *arg)
 {
 	int rc;
 	struct iscsi_conn *conn = arg;
+	bool conn_freed = false;
 
 	/*
 	 * Allow ourselves to be interrupted by SIGINT so that a
@@ -4016,7 +4026,7 @@ int iscsi_target_rx_thread(void *arg)
 	 */
 	rc = wait_for_completion_interruptible(&conn->rx_login_comp);
 	if (rc < 0 || iscsi_target_check_conn_state(conn))
-		return 0;
+		goto out;
 
 	if (!conn->conn_transport->iscsit_get_rx_pdu)
 		return 0;
@@ -4025,7 +4035,15 @@ int iscsi_target_rx_thread(void *arg)
 
 	if (!signal_pending(current))
 		atomic_set(&conn->transport_failed, 1);
-	iscsit_take_action_for_connection_exit(conn);
+	iscsit_take_action_for_connection_exit(conn, &conn_freed);
+
+out:
+	if (!conn_freed) {
+		while (!kthread_should_stop()) {
+			msleep(100);
+		}
+	}
+
 	return 0;
 }
 

drivers/target/iscsi/iscsi_target_erl0.c

@@ -930,8 +930,10 @@ static void iscsit_handle_connection_cleanup(struct iscsi_conn *conn)
 	}
 }
 
-void iscsit_take_action_for_connection_exit(struct iscsi_conn *conn)
+void iscsit_take_action_for_connection_exit(struct iscsi_conn *conn, bool *conn_freed)
 {
+	*conn_freed = false;
+
 	spin_lock_bh(&conn->state_lock);
 	if (atomic_read(&conn->connection_exit)) {
 		spin_unlock_bh(&conn->state_lock);
@@ -942,6 +944,7 @@ void iscsit_take_action_for_connection_exit(struct iscsi_conn *conn)
 	if (conn->conn_state == TARG_CONN_STATE_IN_LOGOUT) {
 		spin_unlock_bh(&conn->state_lock);
 		iscsit_close_connection(conn);
+		*conn_freed = true;
 		return;
 	}
 
@@ -955,4 +958,5 @@ void iscsit_take_action_for_connection_exit(struct iscsi_conn *conn)
 	spin_unlock_bh(&conn->state_lock);
 
 	iscsit_handle_connection_cleanup(conn);
+	*conn_freed = true;
 }

drivers/target/iscsi/iscsi_target_erl0.h

@@ -15,6 +15,6 @@ extern int iscsit_stop_time2retain_timer(struct iscsi_session *);
 extern void iscsit_connection_reinstatement_rcfr(struct iscsi_conn *);
 extern void iscsit_cause_connection_reinstatement(struct iscsi_conn *, int);
 extern void iscsit_fall_back_to_erl0(struct iscsi_session *);
-extern void iscsit_take_action_for_connection_exit(struct iscsi_conn *);
+extern void iscsit_take_action_for_connection_exit(struct iscsi_conn *, bool *);
 
 #endif   /*** ISCSI_TARGET_ERL0_H ***/

drivers/target/iscsi/iscsi_target_login.c

@@ -1464,5 +1464,9 @@ int iscsi_target_login_thread(void *arg)
 			break;
 	}
 
+	while (!kthread_should_stop()) {
+		msleep(100);
+	}
+
 	return 0;
 }