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d="scan'208";a="441963415" Received: from unknown (HELO [10.239.154.55]) ([10.239.154.55]) by fmsmga002.fm.intel.com with ESMTP; 23 Mar 2021 17:53:35 -0700 Subject: Re: [PATCH v10] i2c: virtio: add a virtio i2c frontend driver To: Viresh Kumar References: <226a8d5663b7bb6f5d06ede7701eedb18d1bafa1.1616493817.git.jie.deng@intel.com> <20210323090108.ygx76exdgzudeeqi@vireshk-i7> <20210323093839.n7cq7f5poebqdwit@vireshk-i7> From: Jie Deng Message-ID: <5a415dbe-8e3b-2731-cc52-19aeadda1a17@intel.com> Date: Wed, 24 Mar 2021 08:53:34 +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: <20210323093839.n7cq7f5poebqdwit@vireshk-i7> Content-Language: en-US Cc: mst@redhat.com, bjorn.andersson@linaro.org, wsa+renesas@sang-engineering.com, linux-i2c@vger.kernel.org, wsa@kernel.org, andriy.shevchenko@linux.intel.com, yu1.wang@intel.com, u.kleine-koenig@pengutronix.de, kblaiech@mellanox.com, virtualization@lists.linux-foundation.org, arnd@arndb.de, stefanha@redhat.com, tali.perry1@gmail.com, conghui.chen@intel.com, loic.poulain@linaro.org, linux-kernel@vger.kernel.org, Sergey.Semin@baikalelectronics.ru, jarkko.nikula@linux.intel.com, shuo.a.liu@intel.com, pbonzini@redhat.com, rppt@kernel.org X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On 2021/3/23 17:38, Viresh Kumar wrote: > On 23-03-21, 14:31, Viresh Kumar wrote: >> On 23-03-21, 22:19, Jie Deng wrote: >>> +static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num) >>> +{ >>> + struct virtio_i2c *vi = i2c_get_adapdata(adap); >>> + struct virtqueue *vq = vi->vq; >>> + struct virtio_i2c_req *reqs; >>> + unsigned long time_left; >>> + int ret, nr; >>> + >>> + reqs = kcalloc(num, sizeof(*reqs), GFP_KERNEL); >>> + if (!reqs) >>> + return -ENOMEM; >>> + >>> + mutex_lock(&vi->lock); >>> + >>> + ret = virtio_i2c_send_reqs(vq, reqs, msgs, num); >>> + if (ret == 0) >>> + goto err_unlock_free; >>> + >>> + nr = ret; >>> + reinit_completion(&vi->completion); >> I think I may have found a possible bug here. This reinit_completion() must >> happen before we call virtio_i2c_send_reqs(). It is certainly possible (surely >> in corner cases) that virtio_i2c_msg_done() may get called right after >> virtio_i2c_send_reqs() and before we were able to call reinit_completion(). And >> in that case we will never see the completion happen at all. >> >>> + virtqueue_kick(vq); > I may have misread this. Can the actually start before virtqueue_kick() is > called ? No. It starts when wait_for_completion_timeout is called. So it should be fine here. > If not, then completion may be fine where it is. > _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization 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 B83F3C433E0 for ; Wed, 24 Mar 2021 00:54:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 79176619D3 for ; Wed, 24 Mar 2021 00:54:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233584AbhCXAxr (ORCPT ); Tue, 23 Mar 2021 20:53:47 -0400 Received: from mga02.intel.com ([134.134.136.20]:7887 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230475AbhCXAxm (ORCPT ); Tue, 23 Mar 2021 20:53:42 -0400 IronPort-SDR: CYMrWmbvxZy44HCxByZFaFBFSK5TdUB6DCDzcrLsMx5nlihYx5GryCzUqslKOZJUr5Y+mKUeir JSjYNQbvcZUg== X-IronPort-AV: E=McAfee;i="6000,8403,9932"; a="177716282" X-IronPort-AV: E=Sophos;i="5.81,272,1610438400"; d="scan'208";a="177716282" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Mar 2021 17:53:41 -0700 IronPort-SDR: AYUOOpG1XUognPuZnimdo4CPPCLZYHUifyfk2hiTiY9LSTG4F2iUFi/YfSHAzbNwsVCNuobBS5 8XOkYFitOEpw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.81,272,1610438400"; d="scan'208";a="441963415" Received: from unknown (HELO [10.239.154.55]) ([10.239.154.55]) by fmsmga002.fm.intel.com with ESMTP; 23 Mar 2021 17:53:35 -0700 Subject: Re: [PATCH v10] i2c: virtio: add a virtio i2c frontend driver To: 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: <226a8d5663b7bb6f5d06ede7701eedb18d1bafa1.1616493817.git.jie.deng@intel.com> <20210323090108.ygx76exdgzudeeqi@vireshk-i7> <20210323093839.n7cq7f5poebqdwit@vireshk-i7> From: Jie Deng Message-ID: <5a415dbe-8e3b-2731-cc52-19aeadda1a17@intel.com> Date: Wed, 24 Mar 2021 08:53:34 +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: <20210323093839.n7cq7f5poebqdwit@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-kernel@vger.kernel.org On 2021/3/23 17:38, Viresh Kumar wrote: > On 23-03-21, 14:31, Viresh Kumar wrote: >> On 23-03-21, 22:19, Jie Deng wrote: >>> +static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num) >>> +{ >>> + struct virtio_i2c *vi = i2c_get_adapdata(adap); >>> + struct virtqueue *vq = vi->vq; >>> + struct virtio_i2c_req *reqs; >>> + unsigned long time_left; >>> + int ret, nr; >>> + >>> + reqs = kcalloc(num, sizeof(*reqs), GFP_KERNEL); >>> + if (!reqs) >>> + return -ENOMEM; >>> + >>> + mutex_lock(&vi->lock); >>> + >>> + ret = virtio_i2c_send_reqs(vq, reqs, msgs, num); >>> + if (ret == 0) >>> + goto err_unlock_free; >>> + >>> + nr = ret; >>> + reinit_completion(&vi->completion); >> I think I may have found a possible bug here. This reinit_completion() must >> happen before we call virtio_i2c_send_reqs(). It is certainly possible (surely >> in corner cases) that virtio_i2c_msg_done() may get called right after >> virtio_i2c_send_reqs() and before we were able to call reinit_completion(). And >> in that case we will never see the completion happen at all. >> >>> + virtqueue_kick(vq); > I may have misread this. Can the actually start before virtqueue_kick() is > called ? No. It starts when wait_for_completion_timeout is called. So it should be fine here. > If not, then completion may be fine where it is. >