gfs2: incorrect check for debugfs returns

debugfs_create_dir and debugfs_create_file may return -ENODEV when debugfs
is not configured, so the return value should be checked against ERROR_VALUE
as well, otherwise the later dereference of the dentry pointer would crash
the kernel.
Signed-off-by: Chengyu Song <csong84@gatech.edu>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Acked-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/glock.c

@@ -2047,34 +2047,41 @@ static const struct file_operations gfs2_sbstats_fops = {
 
 int gfs2_create_debugfs_file(struct gfs2_sbd *sdp)
 {
-	sdp->debugfs_dir = debugfs_create_dir(sdp->sd_table_name, gfs2_root);
-	if (!sdp->debugfs_dir)
-		return -ENOMEM;
-	sdp->debugfs_dentry_glocks = debugfs_create_file("glocks",
+	struct dentry *dent;
+
+	dent = debugfs_create_dir(sdp->sd_table_name, gfs2_root);
+	if (IS_ERR_OR_NULL(dent))
+		goto fail;
+	sdp->debugfs_dir = dent;
+
+	dent = debugfs_create_file("glocks",
 				   S_IFREG | S_IRUGO,
 				   sdp->debugfs_dir, sdp,
 				   &gfs2_glocks_fops);
-	if (!sdp->debugfs_dentry_glocks)
+	if (IS_ERR_OR_NULL(dent))
 		goto fail;
+	sdp->debugfs_dentry_glocks = dent;
 
-	sdp->debugfs_dentry_glstats = debugfs_create_file("glstats",
+	dent = debugfs_create_file("glstats",
 				   S_IFREG | S_IRUGO,
 				   sdp->debugfs_dir, sdp,
 				   &gfs2_glstats_fops);
-	if (!sdp->debugfs_dentry_glstats)
+	if (IS_ERR_OR_NULL(dent))
 		goto fail;
+	sdp->debugfs_dentry_glstats = dent;
 
-	sdp->debugfs_dentry_sbstats = debugfs_create_file("sbstats",
+	dent = debugfs_create_file("sbstats",
 				   S_IFREG | S_IRUGO,
 				   sdp->debugfs_dir, sdp,
 				   &gfs2_sbstats_fops);
-	if (!sdp->debugfs_dentry_sbstats)
+	if (IS_ERR_OR_NULL(dent))
 		goto fail;
+	sdp->debugfs_dentry_sbstats = dent;
 
 	return 0;
 fail:
 	gfs2_delete_debugfs_file(sdp);
-	return -ENOMEM;
+	return dent ? PTR_ERR(dent) : -ENOMEM;
 }
 
 void gfs2_delete_debugfs_file(struct gfs2_sbd *sdp)
@@ -2100,6 +2107,8 @@ void gfs2_delete_debugfs_file(struct gfs2_sbd *sdp)
 int gfs2_register_debugfs(void)
 {
 	gfs2_root = debugfs_create_dir("gfs2", NULL);
+	if (IS_ERR(gfs2_root))
+		return PTR_ERR(gfs2_root);
 	return gfs2_root ? 0 : -ENOMEM;
 }