uml: fix previous request size limit fix

The previous patch which limited the number of sectors in a single request
to a COWed device was correct in concept, but the limit was implemented in
the wrong place.

By putting it in ubd_add, it covered the cases where the COWing was
specified on the command line.  However, when the command line only has the
COW file specified, the fact that it's a COW file isn't known until it's
opened, so the limit is missed in these cases.

This patch moves the sector limit from ubd_add to ubd_open_dev.
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/drivers/ubd_kern.c

@@ -612,6 +612,8 @@ static int ubd_open_dev(struct ubd *ubd_dev)
 	ubd_dev->fd = fd;
 
 	if(ubd_dev->cow.file != NULL){
+		blk_queue_max_sectors(ubd_dev->queue, 8 * sizeof(long));
+
 		err = -ENOMEM;
 		ubd_dev->cow.bitmap = (void *) vmalloc(ubd_dev->cow.bitmap_len);
 		if(ubd_dev->cow.bitmap == NULL){
@@ -712,8 +714,6 @@ static int ubd_add(int n, char **error_out)
 	ubd_dev->queue->queuedata = ubd_dev;
 
 	blk_queue_max_hw_segments(ubd_dev->queue, MAX_SG);
-	if(ubd_dev->cow.file != NULL)
-		blk_queue_max_sectors(ubd_dev->queue, 8 * sizeof(long));
 	err = ubd_disk_register(MAJOR_NR, ubd_dev->size, n, &ubd_gendisk[n]);
 	if(err){
 		*error_out = "Failed to register device";