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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 C96BDC433E6 for ; Fri, 12 Mar 2021 08:39:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9852764FC9 for ; Fri, 12 Mar 2021 08:39:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232361AbhCLIid (ORCPT ); Fri, 12 Mar 2021 03:38:33 -0500 Received: from mga09.intel.com ([134.134.136.24]:24678 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232439AbhCLIiD (ORCPT ); Fri, 12 Mar 2021 03:38:03 -0500 IronPort-SDR: IQpyTA2Jt5XvDG/RdEdKxlOWEk+rc4dWYyeQIA6cBf++hHMqhuVOMQmX6Ze3+hYsovNSYpMfjv Hipg8Bo/ASqQ== X-IronPort-AV: E=McAfee;i="6000,8403,9920"; a="188899797" X-IronPort-AV: E=Sophos;i="5.81,243,1610438400"; d="scan'208";a="188899797" Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Mar 2021 00:38:02 -0800 IronPort-SDR: 8c9+J2Da86cjcBUqFbvTy/6CkYSZWSBvXbUTgVkMsNsB6EFOhL5iXaiJuVOjmndPwWr3p+TQc7 3GQB1cWtWIcQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.81,243,1610438400"; d="scan'208";a="377644496" Received: from unknown (HELO [10.239.154.55]) ([10.239.154.55]) by fmsmga007.fm.intel.com with ESMTP; 12 Mar 2021 00:37:57 -0800 Subject: Re: [PATCH v7] i2c: virtio: add a virtio i2c frontend driver To: Wolfram Sang , Viresh Kumar Cc: linux-i2c@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, mst@redhat.com, wsa@kernel.org, jasowang@redhat.com, wsa+renesas@sang-engineering.com, andriy.shevchenko@linux.intel.com, conghui.chen@intel.com, arnd@arndb.de, kblaiech@mellanox.com, jarkko.nikula@linux.intel.com, Sergey.Semin@baikalelectronics.ru, rppt@kernel.org, loic.poulain@linaro.org, tali.perry1@gmail.com, u.kleine-koenig@pengutronix.de, bjorn.andersson@linaro.org, yu1.wang@intel.com, shuo.a.liu@intel.com, stefanha@redhat.com, pbonzini@redhat.com References: <20210312061012.slmfnhxe6y5kgrnv@vireshk-i7> <20210312081108.fvqrvb75byurt3lo@vireshk-i7> From: Jie Deng Message-ID: Date: Fri, 12 Mar 2021 16:37:56 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <20210312081108.fvqrvb75byurt3lo@vireshk-i7> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org On 2021/3/12 16:11, Viresh Kumar wrote: > On 12-03-21, 15:51, Jie Deng wrote: >> On 2021/3/12 14:10, Viresh Kumar wrote: >>> I saw your email about wrong version being sent, I already wrote some >>> reviews. Sending them anyway for FWIW :) >>> >>> On 12-03-21, 21:33, Jie Deng wrote: >>>> +struct virtio_i2c { >>>> + struct virtio_device *vdev; >>>> + struct completion completion; >>>> + struct i2c_adapter adap; >>>> + struct mutex lock; >>> As I said in the previous version (Yes, we were both waiting for >>> Wolfram to answer that), this lock shouldn't be required at all. >>> >>> And since none of us have a use-case at hand where we will have a >>> problem without this lock, we should really skip it. We can always >>> come back and add it if we find an issue somewhere. Until then, better >>> to keep it simple. >> The problem is you can't guarantee that adap->algo->master_xfer >> is only called from i2c_transfer. Any function who holds the adapter can >> call >> adap->algo->master_xfer directly. > See my last reply here, (almost) no one in the mainline kernel call it > directly. And perhaps you can consider the caller broken in that case > and so there is no need of an extra lock, unless you have a case that > is broken. > > https://lore.kernel.org/lkml/20210305072903.wtw645rukmqr5hx5@vireshk-i7/ > >> I prefer to avoid potential issues rather >> than >> find a issue then fix. > This is a very hypothetical issue IMHO as the kernel code doesn't have > such a user. There is no need of locks here, else the i2c core won't > have handled it by itself. I'd like to see Wolfram's opinion. Is it safe to remove lock in adap->algo->master_xfer ?