scsi: storvsc: Avoid excessive host scan on controller change

When there are multiple disks attached to the same SCSI controller, the
host may send several VSTOR_OPERATION_REMOVE_DEVICE or
VSTOR_OPERATION_ENUMERATE_BUS messages in a row, to indicate there is a
change on the SCSI controller. In response, storvsc rescans the SCSI
host.

There is no need to do multiple scans on the same host. Fix the code to
do only one scan.

[mkp: applied by hand]

Signed-off-by: Long Li <longli@microsoft.com>
Tested-by: Cathy Avery <cavery@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/storvsc_drv.c

@@ -487,6 +487,8 @@ struct hv_host_device {
 	unsigned char path;
 	unsigned char target;
 	struct workqueue_struct *handle_error_wq;
+	struct work_struct host_scan_work;
+	struct Scsi_Host *host;
 };
 
 struct storvsc_scan_work {
@@ -515,13 +517,12 @@ static void storvsc_device_scan(struct work_struct *work)
 
 static void storvsc_host_scan(struct work_struct *work)
 {
-	struct storvsc_scan_work *wrk;
 	struct Scsi_Host *host;
 	struct scsi_device *sdev;
+	struct hv_host_device *host_device =
+		container_of(work, struct hv_host_device, host_scan_work);
 
-	wrk = container_of(work, struct storvsc_scan_work, work);
-	host = wrk->host;
-
+	host = host_device->host;
 	/*
 	 * Before scanning the host, first check to see if any of the
 	 * currrently known devices have been hot removed. We issue a
@@ -541,8 +542,6 @@ static void storvsc_host_scan(struct work_struct *work)
 	 * Now scan the host to discover LUNs that may have been added.
 	 */
 	scsi_scan_host(host);
-
-	kfree(wrk);
 }
 
 static void storvsc_remove_lun(struct work_struct *work)
@@ -1118,22 +1117,17 @@ static void storvsc_on_receive(struct storvsc_device *stor_device,
 			     struct vstor_packet *vstor_packet,
 			     struct storvsc_cmd_request *request)
 {
-	struct storvsc_scan_work *work;
-
+	struct hv_host_device *host_dev;
 	switch (vstor_packet->operation) {
 	case VSTOR_OPERATION_COMPLETE_IO:
 		storvsc_on_io_completion(stor_device, vstor_packet, request);
 		break;
 
 	case VSTOR_OPERATION_REMOVE_DEVICE:
 	case VSTOR_OPERATION_ENUMERATE_BUS:
-		work = kmalloc(sizeof(struct storvsc_scan_work), GFP_ATOMIC);
-		if (!work)
-			return;
-
-		INIT_WORK(&work->work, storvsc_host_scan);
-		work->host = stor_device->host;
-		schedule_work(&work->work);
+		host_dev = shost_priv(stor_device->host);
+		queue_work(
+			host_dev->handle_error_wq, &host_dev->host_scan_work);
 		break;
 
 	case VSTOR_OPERATION_FCHBA_DATA:
@@ -1746,6 +1740,7 @@ static int storvsc_probe(struct hv_device *device,
 
 	host_dev->port = host->host_no;
 	host_dev->dev = device;
+	host_dev->host = host;
 
 
 	stor_device = kzalloc(sizeof(struct storvsc_device), GFP_KERNEL);
@@ -1814,6 +1809,7 @@ static int storvsc_probe(struct hv_device *device,
 						host->host_no);
 	if (!host_dev->handle_error_wq)
 		goto err_out2;
+	INIT_WORK(&host_dev->host_scan_work, storvsc_host_scan);
 	/* Register the HBA and start the scsi bus scan */
 	ret = scsi_add_host(host, &device->device);
 	if (ret != 0)