GFS2: Fix use-after-free bug on umount (try #2)

This should solve the issue with the previous attempt at fixing this.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 4cae60f..f91eebd 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -1263,17 +1263,21 @@
 static void gfs2_kill_sb(struct super_block *sb)
 {
 	struct gfs2_sbd *sdp = sb->s_fs_info;
-	if (sdp) {
-		gfs2_meta_syncfs(sdp);
-		dput(sdp->sd_root_dir);
-		dput(sdp->sd_master_dir);
-		sdp->sd_root_dir = NULL;
-		sdp->sd_master_dir = NULL;
+
+	if (sdp == NULL) {
+		kill_block_super(sb);
+		return;
 	}
+
+	gfs2_meta_syncfs(sdp);
+	dput(sdp->sd_root_dir);
+	dput(sdp->sd_master_dir);
+	sdp->sd_root_dir = NULL;
+	sdp->sd_master_dir = NULL;
 	shrink_dcache_sb(sb);
 	kill_block_super(sb);
-	if (sdp)
-		gfs2_delete_debugfs_file(sdp);
+	gfs2_delete_debugfs_file(sdp);
+	kfree(sdp);
 }
 
 struct file_system_type gfs2_fs_type = {