From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 46EB0C32772 for ; Fri, 19 Aug 2022 21:08:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352191AbiHSVIS (ORCPT ); Fri, 19 Aug 2022 17:08:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46586 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350874AbiHSVIQ (ORCPT ); Fri, 19 Aug 2022 17:08:16 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6E29F2186; Fri, 19 Aug 2022 14:08:13 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 29E93B82926; Fri, 19 Aug 2022 21:08:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 90D9BC433D7; Fri, 19 Aug 2022 21:08:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1660943290; bh=6yIJjHS2JZBDcDI1TurkDjj2O3UtwWKh20HdULweR4U=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=diIKdZLzUlo2DYSfAH2kJuTr8tm9cdXOAq+DtCll6fsyBEXMv3Tne+eoICil/9SmT zXpwvGvq6TITh8Oyt4fo3IIUcjyf6wAxIZf0El6D1GBFq/OdeZrSiN4usL/tC/Zguk rfjHnGw4XKMtUloaM5zqtw02/H+K8N566lER4Ilc= Date: Fri, 19 Aug 2022 14:08:09 -0700 From: Andrew Morton To: SeongJae Park Cc: badari.pulavarty@intel.com, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] mm/damon/dbgfs: avoid duplicate context directory creation Message-Id: <20220819140809.1e3929fd8f50bfc32cae31d3@linux-foundation.org> In-Reply-To: <20220819171930.16166-1-sj@kernel.org> References: <20220819171930.16166-1-sj@kernel.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 19 Aug 2022 17:19:30 +0000 SeongJae Park wrote: > From: Badari Pulavarty > > When user tries to create a DAMON context via the DAMON debugfs > interface with a name of an already existing context, the context > directory creation silently fails but the context is added in the > internal data structure. As a result, memory could leak and DAMON > cannot be turned on. An example test case is as below: > > # cd /sys/kernel/debug/damon/ > # echo "off" > monitor_on > # echo paddr > target_ids > # echo "abc" > mk_context > # echo "abc" > mk_context > # echo $$ > abc/target_ids > # echo "on" > monitor_on <<< fails > > This commit fixes the issue by checking if the name already exist and > immediately returning '-EEXIST' in the case. > > ... > > --- a/mm/damon/dbgfs.c > +++ b/mm/damon/dbgfs.c > @@ -795,7 +795,7 @@ static void dbgfs_destroy_ctx(struct damon_ctx *ctx) > */ > static int dbgfs_mk_context(char *name) > { > - struct dentry *root, **new_dirs, *new_dir; > + struct dentry *root, **new_dirs, *new_dir, *dir; > struct damon_ctx **new_ctxs, *new_ctx; > > if (damon_nr_running_ctxs()) > @@ -817,6 +817,12 @@ static int dbgfs_mk_context(char *name) > if (!root) > return -ENOENT; > > + dir = debugfs_lookup(name, root); > + if (dir) { > + dput(dir); > + return -EEXIST; > + } > + > new_dir = debugfs_create_dir(name, root); > dbgfs_dirs[dbgfs_nr_ctxs] = new_dir; It would be simpler (and less racy) to check the debugfs_create_dir() return value for IS_ERR()?