oops in sd_shutdown

From: Andries Brouwer <aebr@win.tue.nl>

I see an Oops in the SCSI code, caused by the fact that sdkp is NULL
in sd_shutdown. "How can that be?", you will ask - dev->driver_data was set
in sd_probe. But in my case sd_probe never finished. An insmod usb-storage
hangs forever, or at least for more than six hours, giving ample opportunity
to observe this race between sd_probe and sd_shutdown.
(Of course sd_probe hangs in sd_revalidate disk.)

Perhaps the obvious test is a good idea.
Locking seems meaningless - sd_probe will never finish.

drivers/scsi/sd.c

@@ -1353,10 +1353,14 @@ static int sd_remove(struct device *dev)
 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;
 	struct scsi_request *sreq;
 	int retries, res;
 
+       sdkp = dev_get_drvdata(dev);
+       if (!sdkp)
+               return;         /* this can happen */
+
 	if (!sdp->online || !sdkp->WCE)
 		return;