target: Fix race between iscsi-target connection shutdown + ABORT_TASK

This patch fixes a race in iscsit_release_commands_from_conn() ->
iscsit_free_cmd() -> transport_generic_free_cmd() + wait_for_tasks=1,
where CMD_T_FABRIC_STOP could end up being set after the final
kref_put() is called from core_tmr_abort_task() context.

This results in transport_generic_free_cmd() blocking indefinately
on se_cmd->cmd_wait_comp, because the target_release_cmd_kref()
check for CMD_T_FABRIC_STOP returns false.

To address this bug, make iscsit_release_commands_from_conn()
do list_splice and set CMD_T_FABRIC_STOP early while holding
iscsi_conn->cmd_lock.  Also make iscsit_aborted_task() only
remove iscsi_cmd_t if CMD_T_FABRIC_STOP has not already been
set.

Finally in target_release_cmd_kref(), only honor fabric_stop
if CMD_T_ABORTED has been set.

Cc: Mike Christie <mchristi@redhat.com>
Cc: Quinn Tran <quinn.tran@qlogic.com>
Cc: Himanshu Madhani <himanshu.madhani@qlogic.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: stable@vger.kernel.org # 3.14+
Tested-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target.c

@@ -492,7 +492,8 @@ void iscsit_aborted_task(struct iscsi_conn *conn, struct iscsi_cmd *cmd)
 	bool scsi_cmd = (cmd->iscsi_opcode == ISCSI_OP_SCSI_CMD);
 
 	spin_lock_bh(&conn->cmd_lock);
-	if (!list_empty(&cmd->i_conn_node))
+	if (!list_empty(&cmd->i_conn_node) &&
+	    !(cmd->se_cmd.transport_state & CMD_T_FABRIC_STOP))
 		list_del_init(&cmd->i_conn_node);
 	spin_unlock_bh(&conn->cmd_lock);
 
@@ -4034,6 +4035,7 @@ int iscsi_target_rx_thread(void *arg)
 
 static void iscsit_release_commands_from_conn(struct iscsi_conn *conn)
 {
+	LIST_HEAD(tmp_list);
 	struct iscsi_cmd *cmd = NULL, *cmd_tmp = NULL;
 	struct iscsi_session *sess = conn->sess;
 	/*
@@ -4042,18 +4044,26 @@ static void iscsit_release_commands_from_conn(struct iscsi_conn *conn)
 	 * has been reset -> returned sleeping pre-handler state.
 	 */
 	spin_lock_bh(&conn->cmd_lock);
-	list_for_each_entry_safe(cmd, cmd_tmp, &conn->conn_cmd_list, i_conn_node) {
+	list_splice_init(&conn->conn_cmd_list, &tmp_list);
 
+	list_for_each_entry(cmd, &tmp_list, i_conn_node) {
+		struct se_cmd *se_cmd = &cmd->se_cmd;
+
+		if (se_cmd->se_tfo != NULL) {
+			spin_lock(&se_cmd->t_state_lock);
+			se_cmd->transport_state |= CMD_T_FABRIC_STOP;
+			spin_unlock(&se_cmd->t_state_lock);
+		}
+	}
+	spin_unlock_bh(&conn->cmd_lock);
+
+	list_for_each_entry_safe(cmd, cmd_tmp, &tmp_list, i_conn_node) {
 		list_del_init(&cmd->i_conn_node);
-		spin_unlock_bh(&conn->cmd_lock);
 
 		iscsit_increment_maxcmdsn(cmd, sess);
-
 		iscsit_free_cmd(cmd, true);
 
-		spin_lock_bh(&conn->cmd_lock);
 	}
-	spin_unlock_bh(&conn->cmd_lock);
 }
 
 static void iscsit_stop_timers_for_cmds(

drivers/target/target_core_transport.c

@@ -2559,7 +2559,8 @@ static void target_release_cmd_kref(struct kref *kref)
 	spin_lock_irqsave(&se_sess->sess_cmd_lock, flags);
 
 	spin_lock(&se_cmd->t_state_lock);
-	fabric_stop = (se_cmd->transport_state & CMD_T_FABRIC_STOP);
+	fabric_stop = (se_cmd->transport_state & CMD_T_FABRIC_STOP) &&
+		      (se_cmd->transport_state & CMD_T_ABORTED);
 	spin_unlock(&se_cmd->t_state_lock);
 
 	if (se_cmd->cmd_wait_set || fabric_stop) {