scsi: virtio_scsi: unplug LUNs when events missed

The event handler calls scsi_scan_host() when events are missed, which will
hotplug new LUNs.  However, this function won't remove any unplugged LUNs.
The result is that hotunplug doesn't work properly when the number of
unplugged LUNs exceeds the event queue size (currently 8).

Scan existing LUNs when events are missed to check if they are still
present.  If not, remove them.

Link: https://lore.kernel.org/r/20190905181903.29756-1-mlupfer@ddn.comSigned-off-by: Matt Lupfer <mlupfer@ddn.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/virtio_scsi.c

@@ -30,6 +30,8 @@
 #include <linux/seqlock.h>
 #include <linux/blk-mq-virtio.h>
 
+#include "sd.h"
+
 #define VIRTIO_SCSI_MEMPOOL_SZ 64
 #define VIRTIO_SCSI_EVENT_LEN 8
 #define VIRTIO_SCSI_VQ_BASE 2
@@ -324,6 +326,36 @@ static void virtscsi_handle_param_change(struct virtio_scsi *vscsi,
 	scsi_device_put(sdev);
 }
 
+static void virtscsi_rescan_hotunplug(struct virtio_scsi *vscsi)
+{
+	struct scsi_device *sdev;
+	struct Scsi_Host *shost = virtio_scsi_host(vscsi->vdev);
+	unsigned char scsi_cmd[MAX_COMMAND_SIZE];
+	int result, inquiry_len, inq_result_len = 256;
+	char *inq_result = kmalloc(inq_result_len, GFP_KERNEL);
+
+	shost_for_each_device(sdev, shost) {
+		inquiry_len = sdev->inquiry_len ? sdev->inquiry_len : 36;
+
+		memset(scsi_cmd, 0, sizeof(scsi_cmd));
+		scsi_cmd[0] = INQUIRY;
+		scsi_cmd[4] = (unsigned char) inquiry_len;
+
+		memset(inq_result, 0, inq_result_len);
+
+		result = scsi_execute_req(sdev, scsi_cmd, DMA_FROM_DEVICE,
+					  inq_result, inquiry_len, NULL,
+					  SD_TIMEOUT, SD_MAX_RETRIES, NULL);
+
+		if (result == 0 && inq_result[0] >> 5) {
+			/* PQ indicates the LUN is not attached */
+			scsi_remove_device(sdev);
+		}
+	}
+
+	kfree(inq_result);
+}
+
 static void virtscsi_handle_event(struct work_struct *work)
 {
 	struct virtio_scsi_event_node *event_node =
@@ -335,6 +367,7 @@ static void virtscsi_handle_event(struct work_struct *work)
 	    cpu_to_virtio32(vscsi->vdev, VIRTIO_SCSI_T_EVENTS_MISSED)) {
 		event->event &= ~cpu_to_virtio32(vscsi->vdev,
 						   VIRTIO_SCSI_T_EVENTS_MISSED);
+		virtscsi_rescan_hotunplug(vscsi);
 		scsi_scan_host(virtio_scsi_host(vscsi->vdev));
 	}