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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 93EEDC32771 for ; Fri, 19 Aug 2022 21:16:37 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 19DC06B0073; Fri, 19 Aug 2022 17:16:37 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 14D2B8D0003; Fri, 19 Aug 2022 17:16:37 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 014648D0002; Fri, 19 Aug 2022 17:16:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id E6DE76B0073 for ; Fri, 19 Aug 2022 17:16:36 -0400 (EDT) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id C1450141A6A for ; Fri, 19 Aug 2022 21:16:36 +0000 (UTC) X-FDA: 79817601192.12.6C5AE58 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by imf24.hostedemail.com (Postfix) with ESMTP id 5B84A180029 for ; Fri, 19 Aug 2022 21:16:36 +0000 (UTC) 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 DD129B828EA; Fri, 19 Aug 2022 21:16:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 05B56C433D6; Fri, 19 Aug 2022 21:16:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1660943793; bh=GOhiVfsBqX2y7z90q7076zjMmF36TVkpwUIPXpa8SDU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Y550pgYDKfKcM94iqZr/Kgq976SROYgaTEdPCdGJTjVuM9A8E9QcWgimbBLXTrhgC wFFQeAuB8KcNOT+QpevCOXkINubcBNAPa1d24Q0EBAxU5908J5ExF6xMOcwgxZDNUN OfF9Ohl6YRulDg4I8E9E1kcGPHJ2yCG7Qwf0n7NalTbH08DnVK91ipOBZrpsgsIIaI 5h7yZxM71gpMmuIQjUh353asy0fDMY8F/VJCNC9aoB/cAswa6sDF6nVNMniOi8WrcH eJm1uH+UyCmoqEMAiM9/PlgF9nleEDZlPAKon/5iBGyNTQ/7zdDIQWWp2cub8TYMt9 JYqLUlDZr7G+w== From: SeongJae Park To: Andrew Morton Cc: SeongJae Park , gregkh@linuxfoundation.org, 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 Date: Fri, 19 Aug 2022 21:16:31 +0000 Message-Id: <20220819211631.16658-1-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220819140809.1e3929fd8f50bfc32cae31d3@linux-foundation.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660943796; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=XNRyJKw6pVcefHs8RgmXzxv6AiCGEbt2gjrU0xvplPI=; b=3gnjwC3cJEe5H9YrztDQ7z4MJL+RCJRiEAy/FHkJjU2/XVB2AOirJ31vuiNN9Z6hWbz3M/ RJpl5UaDvX2HrZmqrVb4kIi8ArfEZqW5kgYTiK8HjhaEmFGUcuv/V9huNa76ZAjSyIUAvd bHK/ZTGUSVFxiH4NeJQplGu1swqzAMY= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Y550pgYD; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf24.hostedemail.com: domain of sj@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=sj@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660943796; a=rsa-sha256; cv=none; b=dIcL/prFFBu1gxRpryXnURYOkRHY5panUpcCCdCNbzLbyUsRTKSuBDBp3d/yVBwFsF7T5r jpz5IYjXR6xCAeF6s0PlCWxeVuyXiH8HNlHwiXjSlRZ7/6WGHQXTKP3LdCHMU/WiixMMep +tRwgxiD0hmJArCM5+6vtZ/c5IsjVvY= X-Stat-Signature: eftz3djmfjsfgp1pfnwu9ejqoxfpfeuj X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 5B84A180029 Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Y550pgYD; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf24.hostedemail.com: domain of sj@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=sj@kernel.org X-Rspam-User: X-HE-Tag: 1660943796-326966 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, 19 Aug 2022 14:08:09 -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()? I was merely following Greg's previous advice for ignoring the return value[1] of the function, but I might misunderstanding his intention, so CC-ing Greg. Greg, may I ask your opinion? [1] https://lore.kernel.org/linux-mm/YB1kZaD%2F7omxXztF@kroah.com/ Thanks, SJ