gfs2: Put bitmap buffers in put_super

gfs2_put_super calls gfs2_clear_rgrpd to destroy the gfs2_rgrpd objects
attached to the resource group glocks.  That function should release the
buffers attached to the gfs2_bitmap objects (bi_bh), but the call to
gfs2_rgrp_brelse for doing that is missing.

When gfs2_releasepage later runs across these buffers which are still
referenced, it refuses to free them.  This causes the pages the buffers
are attached to to remain referenced as well.  With enough mount/unmount
cycles, the system will eventually run out of memory.

Fix this by adding the missing call to gfs2_rgrp_brelse in
gfs2_clear_rgrpd.

(Also fix a gfs2_rgrp_relse -> gfs2_rgrp_brelse typo in a comment.)

Fixes: 39b0f1e9 ("GFS2: Don't brelse rgrp buffer_heads every allocation")
Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/rgrp.c

@@ -733,6 +733,7 @@ void gfs2_clear_rgrpd(struct gfs2_sbd *sdp)
 
 		if (gl) {
 			glock_clear_object(gl, rgd);
+			gfs2_rgrp_brelse(rgd);
 			gfs2_glock_put(gl);
 		}
 
@@ -1174,7 +1175,7 @@ static u32 count_unlinked(struct gfs2_rgrpd *rgd)
  * @rgd: the struct gfs2_rgrpd describing the RG to read in
  *
  * Read in all of a Resource Group's header and bitmap blocks.
- * Caller must eventually call gfs2_rgrp_relse() to free the bitmaps.
+ * Caller must eventually call gfs2_rgrp_brelse() to free the bitmaps.
  *
  * Returns: errno
  */