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 X-Spam-Level: X-Spam-Status: No, score=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 58DBCC2D0E9 for ; Sun, 29 Mar 2020 13:46:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2DCFD2073B for ; Sun, 29 Mar 2020 13:46:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=metafoo.de header.i=@metafoo.de header.b="KPclBmXc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728203AbgC2NqY (ORCPT ); Sun, 29 Mar 2020 09:46:24 -0400 Received: from www381.your-server.de ([78.46.137.84]:60640 "EHLO www381.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727903AbgC2NqX (ORCPT ); Sun, 29 Mar 2020 09:46:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=metafoo.de; s=default2002; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=KnCgqqdWyNK62dUdcWZxkpPXuIoCWmgb+CFyMmoZanM=; b=KPclBmXcudrmQ8TN6TD61WVVkC yVD9ejfhiE/AWKXSFZRXUMwtf+CMCycy7ppYJ+hzcvKahpLT3qExBev/ASrRZdyoCJkVbYZj46U/5 gDANJWNErFRwmsT5EgpVw0Kd3wgQpUezyZfT7N0BWtdmfEdVlDVYopMjYCbbbpyDjILdnbU0Iwjl4 fKlgpVolErNwfrSDRc9tNvPGFm6ChDraLGqL08vd9QgZKY6rJED5hMBke1wCDDRk8fFjvutoSDBJi EHqNQygebjSmyVUqrDmUtaVOMk7Vj30JeB//iDT3GmeeoeBQ1OYq41os+saaPa7seMzS4gjU0VZSP LpGa5QOQ==; Received: from sslproxy06.your-server.de ([78.46.172.3]) by www381.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89_1) (envelope-from ) id 1jIYGY-0002vF-Gv; Sun, 29 Mar 2020 15:46:19 +0200 Received: from [82.135.74.134] (helo=[192.168.178.20]) by sslproxy06.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1jIYGY-000RHr-5p; Sun, 29 Mar 2020 15:46:18 +0200 Subject: Re: [PATCH 0/2] use DEFINE_DEBUGFS_ATTRIBUTE instead of DEFINE_SIMPLE_ATTRIBUTE To: Rohit Sarkar , Jonathan Cameron Cc: linux-iio@vger.kernel.org, dragos.bogdan@analog.com, Michael Hennerich , Stefan Popa , Hartmut Knaack , Peter Meerwald-Stadler , linux-kernel@vger.kernel.org, "Ardelean, Alexandru" , zhong jiang References: <20200328063456.24012-1-rohitsarkar5398@gmail.com> <20200329103818.2fce9529@archlinux> <5e8087e3.1c69fb81.13d97.448d@mx.google.com> From: Lars-Peter Clausen Message-ID: <8d861c54-75be-589a-9e71-cd30cbde84d3@metafoo.de> Date: Sun, 29 Mar 2020 15:46:17 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <5e8087e3.1c69fb81.13d97.448d@mx.google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Authenticated-Sender: lars@metafoo.de X-Virus-Scanned: Clear (ClamAV 0.102.2/25765/Sat Mar 28 14:16:42 2020) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/29/20 1:34 PM, Rohit Sarkar wrote: > On Sun, Mar 29, 2020 at 10:38:18AM +0100, Jonathan Cameron wrote: >> On Sat, 28 Mar 2020 12:04:53 +0530 >> Rohit Sarkar wrote: >> >>> The debugfs_create_file_unsafe method does not protect the fops given to >>> it from file removal. It must be used with DEFINE_DEBUGFS_ATTRIBUTE >>> which makes the fops aware of the file lifetime. >>> >>> Further using DEFINE_DEBUGFS_ATTRIBUTE along with >>> debugfs_create_file_unsafe significantly reduces the overhead introduced by >>> debugfs_create_file which creates a lifetime managing proxy around each >>> fops handed in. Refer [1] for more on this. >>> >>> Fixes the following warnings reported by coccinelle: >>> drivers/iio/imu//adis16460.c:126:0-23: WARNING: adis16460_flash_count_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE >>> drivers/iio/imu//adis16460.c:108:0-23: WARNING: adis16460_product_id_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE >>> drivers/iio/imu//adis16460.c:90:0-23: WARNING: adis16460_serial_number_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE >>> drivers/iio/imu//adis16400.c:278:0-23: WARNING: adis16400_flash_count_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE >>> drivers/iio/imu//adis16400.c:261:0-23: WARNING: adis16400_product_id_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE >>> >>> [1]: https://lists.gt.net/linux/kernel/2369498 >>> >>> Rohit Sarkar (2): >>> iio: imu: adis16400: use DEFINE_DEBUGFS_ATTRIBUTE instead of >>> DEFINE_SIMPLE_ATTRIBUTE >>> iio: imu: adis16460: use DEFINE_DEBUGFS_ATTRIBUTE instead of >>> DEFINE_SIMPLE_ATTRIBUTE >>> >>> drivers/iio/imu/adis16400.c | 4 ++-- >>> drivers/iio/imu/adis16460.c | 6 +++--- >>> 2 files changed, 5 insertions(+), 5 deletions(-) >>> >> Hi Rohit, > Hey, >> You've opened a can of worms with this one. There as a previous series >> posted doing exactly this change back in 2019 by Zhong Jiang (cc'd) >> >> At the time I did a bit of looking into why this had been universally taken >> up cross tree and turned out there are some potential issues. >> >> Alexandru added it to the list of things to test, but I guess it got >> buried under other work and is still outstanding. >> >> https://lkml.org/lkml/2019/10/30/144 > Acc. to the patch by Zhong this change kind of comes off as a cosmetic > change as in the commit message he mentions "it is more clear". > > But there is certainly more to it than that: > In the current scenario since we are using debugfs_create_file_unsafe > the file has no protection whatsoever against removal. The drivers you are patching all use debugfs_create_file() as far as I can see. The way I understand it using DEFINE_DEBUGFS_ATTRIBUTE without switching to debugfs_create_file_unsafe() will not make a difference. There will only be more overhead since the files are protected twice. - Lars