gfs2: Convert to properly refcounting bdi

Similarly to set_bdev_super() GFS2 just used block device reference to
bdi. Convert it to properly getting bdi reference. The reference will
get automatically dropped on superblock destruction.

CC: Steven Whitehouse <swhiteho@redhat.com>
CC: Bob Peterson <rpeterso@redhat.com>
CC: cluster-devel@redhat.com
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: NJens Axboe <axboe@fb.com>

fs/gfs2/ops_fstype.c

@@ -23,6 +23,7 @@
 #include <linux/quotaops.h>
 #include <linux/lockdep.h>
 #include <linux/module.h>
+#include <linux/backing-dev.h>
 
 #include "gfs2.h"
 #include "incore.h"
@@ -1222,12 +1223,8 @@ static int set_gfs2_super(struct super_block *s, void *data)
 {
 	s->s_bdev = data;
 	s->s_dev = s->s_bdev->bd_dev;
-
-	/*
-	 * We set the bdi here to the queue backing, file systems can
-	 * overwrite this in ->fill_super()
-	 */
-	s->s_bdi = bdev_get_queue(s->s_bdev)->backing_dev_info;
+	s->s_bdi = bdi_get(s->s_bdev->bd_bdi);
+	s->s_iflags |= SB_I_DYNBDI;
 	return 0;
 }