scsi: hisi_sas: fix NULL deference when TMF timeouts

If a TMF timeouts (maybe due to unlikely scenario of an expander being
unplugged when TMF for remote device is active), when we eventually try
to free the slot, we crash as we dereference the slot's task, which has
already been released.

As a fix, add checks in the slot release code for a NULL task.
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/hisi_sas/hisi_sas_main.c

@@ -77,18 +77,23 @@ static void hisi_sas_slot_index_init(struct hisi_hba *hisi_hba)
 void hisi_sas_slot_task_free(struct hisi_hba *hisi_hba, struct sas_task *task,
 			     struct hisi_sas_slot *slot)
 {
+
+	if (task) {
 		struct device *dev = &hisi_hba->pdev->dev;
 		struct domain_device *device = task->dev;
 		struct hisi_sas_device *sas_dev = device->lldd_dev;
 
-	if (!slot->task)
-		return;
-
 		if (!sas_protocol_ata(task->task_proto))
 			if (slot->n_elem)
 				dma_unmap_sg(dev, task->scatter, slot->n_elem,
 					     task->data_dir);
 
+		task->lldd_task = NULL;
+
+		if (sas_dev)
+			atomic64_dec(&sas_dev->running_req);
+	}
+
 	if (slot->command_table)
 		dma_pool_free(hisi_hba->command_table_pool,
 			      slot->command_table, slot->command_table_dma);
@@ -102,12 +107,10 @@ void hisi_sas_slot_task_free(struct hisi_hba *hisi_hba, struct sas_task *task,
 			      slot->sge_page_dma);
 
 	list_del_init(&slot->entry);
-	task->lldd_task = NULL;
 	slot->task = NULL;
 	slot->port = NULL;
 	hisi_sas_slot_index_free(hisi_hba, slot->idx);
-	if (sas_dev)
-		atomic64_dec(&sas_dev->running_req);
+
 	/* slot memory is fully zeroed when it is reused */
 }
 EXPORT_SYMBOL_GPL(hisi_sas_slot_task_free);
@@ -569,15 +572,12 @@ static void hisi_sas_port_notify_formed(struct asd_sas_phy *sas_phy)
 	spin_unlock_irqrestore(&hisi_hba->lock, flags);
 }
 
-static void hisi_sas_do_release_task(struct hisi_hba *hisi_hba,
-				     struct sas_task *task,
+static void hisi_sas_do_release_task(struct hisi_hba *hisi_hba, struct sas_task *task,
 				     struct hisi_sas_slot *slot)
 {
-	struct task_status_struct *ts;
+	if (task) {
 		unsigned long flags;
-
-	if (!task)
-		return;
+		struct task_status_struct *ts;
 
 		ts = &task->task_status;
 
@@ -588,6 +588,7 @@ static void hisi_sas_do_release_task(struct hisi_hba *hisi_hba,
 			~(SAS_TASK_STATE_PENDING | SAS_TASK_AT_INITIATOR);
 		task->task_state_flags |= SAS_TASK_STATE_DONE;
 		spin_unlock_irqrestore(&task->task_state_lock, flags);
+	}
 
 	hisi_sas_slot_task_free(hisi_hba, task, slot);
 }
@@ -742,7 +743,12 @@ static int hisi_sas_exec_internal_tmf_task(struct domain_device *device,
 		/* Even TMF timed out, return direct. */
 		if ((task->task_state_flags & SAS_TASK_STATE_ABORTED)) {
 			if (!(task->task_state_flags & SAS_TASK_STATE_DONE)) {
+				struct hisi_sas_slot *slot = task->lldd_task;
+
 				dev_err(dev, "abort tmf: TMF task timeout\n");
+				if (slot)
+					slot->task = NULL;
+
 				goto ex_err;
 			}
 		}