GFS2: Update to AIL list locking

The previous patch missed a couple of places where the AIL list
needed locking, so this fixes up those places, plus a comment
is corrected too.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Cc: Dave Chinner <dchinner@redhat.com>
diff --git a/fs/gfs2/meta_io.c b/fs/gfs2/meta_io.c
index 939739c..01d97f4 100644
--- a/fs/gfs2/meta_io.c
+++ b/fs/gfs2/meta_io.c
@@ -326,6 +326,7 @@
 		brelse(bh);
 	}
 	if (bd) {
+		spin_lock(&sdp->sd_ail_lock);
 		if (bd->bd_ail) {
 			gfs2_remove_from_ail(bd);
 			bh->b_private = NULL;
@@ -333,6 +334,7 @@
 			bd->bd_blkno = bh->b_blocknr;
 			gfs2_trans_add_revoke(sdp, bd);
 		}
+		spin_unlock(&sdp->sd_ail_lock);
 	}
 	clear_buffer_dirty(bh);
 	clear_buffer_uptodate(bh);