[PATCH] md: don't allow new md/bitmap file to be set if one already exists

... otherwise we loose a reference and can never free the file.
Signed-off-by: NNeil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

drivers/md/md.c

@@ -2430,7 +2430,7 @@ static int set_bitmap_file(mddev_t *mddev, int fd)
 {
 	int err;
 
-	if (mddev->pers)
+	if (mddev->pers || mddev->bitmap_file)
 		return -EBUSY;
 
 	mddev->bitmap_file = fget(fd);