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=-15.5 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_2 autolearn=unavailable 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 2889EC432BE for ; Sat, 31 Jul 2021 17:49:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 092DA61054 for ; Sat, 31 Jul 2021 17:49:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230479AbhGaRto (ORCPT ); Sat, 31 Jul 2021 13:49:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:48888 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229830AbhGaRtn (ORCPT ); Sat, 31 Jul 2021 13:49:43 -0400 Received: from jic23-huawei (cpc108967-cmbg20-2-0-cust86.5-4.cable.virginm.net [81.101.6.87]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 11CD661042; Sat, 31 Jul 2021 17:49:31 +0000 (UTC) Date: Sat, 31 Jul 2021 18:52:10 +0100 From: Jonathan Cameron To: "hui.liu" Cc: , , , , , , , , , , , , , , Subject: Re: [PATCH] iio: mtk-auxadc: add mutex_destroy Message-ID: <20210731185210.7acb5f79@jic23-huawei> In-Reply-To: <1627300994.11261.11.camel@mhfsdcap03> References: <20210715093523.29844-1-hui.liu@mediatek.com> <20210715093523.29844-2-hui.liu@mediatek.com> <20210717174432.7e69e4e9@jic23-huawei> <1627042875.27985.15.camel@mhfsdcap03> <20210724183003.6f3bc1d5@jic23-huawei> <1627300994.11261.11.camel@mhfsdcap03> X-Mailer: Claws Mail 4.0.0 (GTK+ 3.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Mon, 26 Jul 2021 20:03:14 +0800 hui.liu wrote: > On Sat, 2021-07-24 at 18:30 +0100, Jonathan Cameron wrote: > > On Fri, 23 Jul 2021 20:21:15 +0800 > > hui.liu wrote: > > > > > On Sat, 2021-07-17 at 17:44 +0100, Jonathan Cameron wrote: > > > > On Thu, 15 Jul 2021 17:35:23 +0800 > > > > Hui Liu wrote: > > > > > > > > > Add mutex_destroy when probe fail and remove device. > > > > > > > > > > Signed-off-by: Hui Liu > > > > Hi Hui Liu, > > > > > > > > We very very rarely bother to call mutex_destroy(). The reason is > > > > that it is only a non noop in when mutex debugging is enabled and > > > > that is only useful if there is a plausible route in which it could > > > > be used after the mutex_destroy. Given these are both at the ends > > > > of removal paths, I don't think this is useful. That's why you will > > > > rarely find mutex_destroy() being called. > > > > > > > > Thanks, > > > > > > > > Jonathan > > > > > > Hi Jonathon, > > > > > > I think this patch could assurance the integrity of code. > > > mutex_init will be called when driver probe. If driver probe fail or > > > device removed, mutex_destroy could set lock->magic to NULL. > > > > I'm not seeing the use case here given the location doesn't leave > > a huge amount of code that could have such a bug. There might have been > > something if we had any route to increment the reference count of the > > structure this mutex is ultimately embedded in and so have it outlast > > the remove function or error path. In this driver it looks like there is > > no such path. Hence you are protecting against a automated > > cleanup of core code (nothing in the driver itself) which is obviously > > not going to try taking a driver specific mutex. > > > > A few side notes: > > > > You are calling it wrong place in remove. The ordering in remove > > should be the opposite of that in probe so the mutex_destroy should either > > be a few lines earlier, or you should have a comment there to say why you > > are doing it where you have chosen to do so. > > > > The style of this probe is to do error handling in a block at the end. > > So this handling should be there, not in the if statement. > > > > Jonathan > > > > > Hi Jonathon, > > Base on your helpful opinion, We will to do two changes in patch v2. > 1. In probe: move mutex_destroy from the if statement to error handling > path(err_power_off). > 2. In remove: calling mutex_destroy right after iio_device_unregister. > > Do we need some more change? Thanks. Ah. Sorry I missed this in the flood of emails during the week. Anyhow, I've replied to the v1 posting. Jonathan > > > > > > > > Thanks. > > > Hui > > > > > > > > > > > > --- > > > > > drivers/iio/adc/mt6577_auxadc.c | 2 ++ > > > > > 1 file changed, 2 insertions(+) > > > > > > > > > > diff --git a/drivers/iio/adc/mt6577_auxadc.c b/drivers/iio/adc/mt6577_auxadc.c > > > > > index 79c1dd68b909..d57243037ad6 100644 > > > > > --- a/drivers/iio/adc/mt6577_auxadc.c > > > > > +++ b/drivers/iio/adc/mt6577_auxadc.c > > > > > @@ -289,6 +289,7 @@ static int mt6577_auxadc_probe(struct platform_device *pdev) > > > > > ret = iio_device_register(indio_dev); > > > > > if (ret < 0) { > > > > > dev_err(&pdev->dev, "failed to register iio device\n"); > > > > > + mutex_destroy(&adc_dev->lock); > > > > > goto err_power_off; > > > > > } > > > > > > > > > > @@ -313,6 +314,7 @@ static int mt6577_auxadc_remove(struct platform_device *pdev) > > > > > 0, MT6577_AUXADC_PDN_EN); > > > > > > > > > > clk_disable_unprepare(adc_dev->adc_clk); > > > > > + mutex_destroy(&adc_dev->lock); > > > > > > > > > > return 0; > > > > > } > > > > > > > > > >