target: Fix quiese during transport_write_pending_qf endless loop

This patch fixes a potential end-less loop during QUEUE_FULL,
where cmd->se_tfo->write_pending() callback fails repeatedly
but __transport_wait_for_tasks() has already been invoked to
quiese the outstanding se_cmd descriptor.

To address this bug, this patch adds a CMD_T_STOP|CMD_T_ABORTED
check within transport_write_pending_qf() and invokes the
existing se_cmd->t_transport_stop_comp to signal quiese
completion back to __transport_wait_for_tasks().

Cc: Mike Christie <mchristi@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Cc: Michael Cyr <mikecyr@linux.vnet.ibm.com>
Cc: Potnuri Bharat Teja <bharat@chelsio.com>
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: stable@vger.kernel.org # 4.11+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_transport.c

@@ -2560,7 +2560,20 @@ EXPORT_SYMBOL(transport_generic_new_cmd);
 
 static void transport_write_pending_qf(struct se_cmd *cmd)
 {
+	unsigned long flags;
 	int ret;
+	bool stop;
+
+	spin_lock_irqsave(&cmd->t_state_lock, flags);
+	stop = (cmd->transport_state & (CMD_T_STOP | CMD_T_ABORTED));
+	spin_unlock_irqrestore(&cmd->t_state_lock, flags);
+
+	if (stop) {
+		pr_debug("%s:%d CMD_T_STOP|CMD_T_ABORTED for ITT: 0x%08llx\n",
+			__func__, __LINE__, cmd->tag);
+		complete_all(&cmd->t_transport_stop_comp);
+		return;
+	}
 
 	ret = cmd->se_tfo->write_pending(cmd);
 	if (ret) {