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 5BC5BC00140 for ; Sun, 21 Aug 2022 06:58:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229762AbiHUG6g (ORCPT ); Sun, 21 Aug 2022 02:58:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47352 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229725AbiHUG61 (ORCPT ); Sun, 21 Aug 2022 02:58:27 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 63E112ADE; Sat, 20 Aug 2022 23:58:24 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 0017060CD4; Sun, 21 Aug 2022 06:58:24 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6D12EC433D6; Sun, 21 Aug 2022 06:58:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1661065103; bh=tbuVzHoEL8ZVZPHiH4E6B7fj2SIHZgFp4d15ptne13A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=qeS88CcrbZxYoNjnNZ8rrfUJAL0QH8+Ilq9eUT2AWxAB/JeIQ5ONfou68r+J8agdD Kd2kevU/0A4V3wpOZAv32UzCjcexHXYMLyYAa4cWfNDtwWKtddQxNh5ADur/eZP5vj CHtkQ+AHGAuqFb0t0Z4ZBk6MTfI66ufO+p5Glitw= Date: Sat, 20 Aug 2022 19:32:37 +0200 From: Greg KH To: Andrew Morton Cc: SeongJae Park , 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: References: <20220819171930.16166-1-sj@kernel.org> <20220819140809.1e3929fd8f50bfc32cae31d3@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220819140809.1e3929fd8f50bfc32cae31d3@linux-foundation.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 19, 2022 at 02:08:09PM -0700, Andrew Morton wrote: > 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()? > Yes, if you _HAVE_ to know if the code works properly (i.e. because your feature totally depends on debugfs like damon does), or you have a potential duplicate name like this, then sure, check the return value and do something based on it. It's odd enough that you should put a comment above the check just so I don't go and send a patch to delete it later on :) thanks, greg k-h