[SCSI] sd: Fix refcounting

Currently the driver takes a reference only for requests coming by way
of the gendisk, not for requests coming by way of the struct device or
struct scsi_device.  Such requests can arrive in the rescan, flush,
and shutdown pathways.

The patch also makes the scsi_disk keep a reference to the underlying
scsi_device, and it erases the scsi_device's pointer to the scsi_disk
when the scsi_device is removed (since the pointer should no longer be
used).

This resolves Bugzilla entry #5237.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/sd.c

@@ -177,24 +177,38 @@ static inline struct scsi_disk *scsi_disk(struct gendisk *disk)
 	return container_of(disk->private_data, struct scsi_disk, driver);
 }
 
-static struct scsi_disk *scsi_disk_get(struct gendisk *disk)
+static struct scsi_disk *__scsi_disk_get(struct gendisk *disk)
 {
 	struct scsi_disk *sdkp = NULL;
 
-	down(&sd_ref_sem);
-	if (disk->private_data == NULL)
-		goto out;
+	if (disk->private_data) {
 		sdkp = scsi_disk(disk);
+		if (scsi_device_get(sdkp->device) == 0)
 			kref_get(&sdkp->kref);
-	if (scsi_device_get(sdkp->device))
-		goto out_put;
+		else
+			sdkp = NULL;
+	}
+	return sdkp;
+}
+
+static struct scsi_disk *scsi_disk_get(struct gendisk *disk)
+{
+	struct scsi_disk *sdkp;
+
+	down(&sd_ref_sem);
+	sdkp = __scsi_disk_get(disk);
 	up(&sd_ref_sem);
 	return sdkp;
+}
 
- out_put:
-	kref_put(&sdkp->kref, scsi_disk_release);
-	sdkp = NULL;
- out:
+static struct scsi_disk *scsi_disk_get_from_dev(struct device *dev)
+{
+	struct scsi_disk *sdkp;
+
+	down(&sd_ref_sem);
+	sdkp = dev_get_drvdata(dev);
+	if (sdkp)
+		sdkp = __scsi_disk_get(sdkp->disk);
 	up(&sd_ref_sem);
 	return sdkp;
 }
@@ -716,16 +730,17 @@ static int sd_sync_cache(struct scsi_device *sdp)
 
 static int sd_issue_flush(struct device *dev, sector_t *error_sector)
 {
+	int ret = 0;
 	struct scsi_device *sdp = to_scsi_device(dev);
-	struct scsi_disk *sdkp = dev_get_drvdata(dev);
+	struct scsi_disk *sdkp = scsi_disk_get_from_dev(dev);
 
 	if (!sdkp)
                return -ENODEV;
 
-	if (!sdkp->WCE)
-		return 0;
-
-	return sd_sync_cache(sdp);
+	if (sdkp->WCE)
+		ret = sd_sync_cache(sdp);
+	scsi_disk_put(sdkp);
+	return ret;
 }
 
 static void sd_end_flush(request_queue_t *q, struct request *flush_rq)
@@ -754,23 +769,30 @@ static void sd_end_flush(request_queue_t *q, struct request *flush_rq)
 static int sd_prepare_flush(request_queue_t *q, struct request *rq)
 {
 	struct scsi_device *sdev = q->queuedata;
-	struct scsi_disk *sdkp = dev_get_drvdata(&sdev->sdev_gendev);
+	struct scsi_disk *sdkp = scsi_disk_get_from_dev(&sdev->sdev_gendev);
+	int ret = 0;
 
+	if (sdkp) {
 		if (sdkp->WCE) {
 			memset(rq->cmd, 0, sizeof(rq->cmd));
 			rq->flags |= REQ_BLOCK_PC | REQ_SOFTBARRIER;
 			rq->timeout = SD_TIMEOUT;
 			rq->cmd[0] = SYNCHRONIZE_CACHE;
-		return 1;
+			ret = 1;
 		}
-
-	return 0;
+		scsi_disk_put(sdkp);
+	}
+	return ret;
 }
 
 static void sd_rescan(struct device *dev)
 {
-	struct scsi_disk *sdkp = dev_get_drvdata(dev);
+	struct scsi_disk *sdkp = scsi_disk_get_from_dev(dev);
+
+	if (sdkp) {
 		sd_revalidate_disk(sdkp->disk);
+		scsi_disk_put(sdkp);
+	}
 }
 
 
@@ -1561,6 +1583,7 @@ static int sd_probe(struct device *dev)
 	if (error)
 		goto out_put;
 
+	get_device(&sdp->sdev_gendev);
 	sdkp->device = sdp;
 	sdkp->driver = &sd_template;
 	sdkp->disk = gd;
@@ -1637,7 +1660,9 @@ static int sd_remove(struct device *dev)
 
 	del_gendisk(sdkp->disk);
 	sd_shutdown(dev);
+
 	down(&sd_ref_sem);
+	dev_set_drvdata(dev, NULL);
 	kref_put(&sdkp->kref, scsi_disk_release);
 	up(&sd_ref_sem);
 
@@ -1663,8 +1688,8 @@ static void scsi_disk_release(struct kref *kref)
 	spin_unlock(&sd_index_lock);
 
 	disk->private_data = NULL;
-
 	put_disk(disk);
+	put_device(&sdkp->device->sdev_gendev);
 
 	kfree(sdkp);
 }
@@ -1677,17 +1702,17 @@ static void scsi_disk_release(struct kref *kref)
 static void sd_shutdown(struct device *dev)
 {
 	struct scsi_device *sdp = to_scsi_device(dev);
-	struct scsi_disk *sdkp = dev_get_drvdata(dev);
+	struct scsi_disk *sdkp = scsi_disk_get_from_dev(dev);
 
 	if (!sdkp)
 		return;         /* this can happen */
 
-	if (!sdkp->WCE)
-		return;
-
+	if (sdkp->WCE) {
 		printk(KERN_NOTICE "Synchronizing SCSI cache for disk %s: \n",
 				sdkp->disk->disk_name);
 		sd_sync_cache(sdp);
+	}
+	scsi_disk_put(sdkp);
 }
 
 /**