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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2AB3CC4332F for ; Wed, 19 Oct 2022 07:18:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229939AbiJSHSM (ORCPT ); Wed, 19 Oct 2022 03:18:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41702 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229872AbiJSHSH (ORCPT ); Wed, 19 Oct 2022 03:18:07 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6CDD574E1B for ; Wed, 19 Oct 2022 00:18:02 -0700 (PDT) Received: from dggemv703-chm.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4Mshp05zszzJn5w; Wed, 19 Oct 2022 15:15:20 +0800 (CST) Received: from kwepemm600005.china.huawei.com (7.193.23.191) by dggemv703-chm.china.huawei.com (10.3.19.46) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Wed, 19 Oct 2022 15:17:46 +0800 Received: from [10.67.103.158] (10.67.103.158) by kwepemm600005.china.huawei.com (7.193.23.191) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Wed, 19 Oct 2022 15:17:45 +0800 Subject: Re: [Linuxarm] [PATCH 1/2] hisi_acc_vfio_pci: Add debugfs to migration driver To: Jason Gunthorpe CC: John Garry , , , , , References: <20221014025757.39415-1-liulongfang@huawei.com> <20221014025757.39415-2-liulongfang@huawei.com> <42d12308-4777-47a7-a1ae-50dfada050cf@huawei.com> <7c041671-71bf-d558-d47a-70296fe5c30e@huawei.com> <9826a418-4a14-aa4a-9eb8-6faf3e43c8e3@huawei.com> From: liulongfang Message-ID: Date: Wed, 19 Oct 2022 15:17:44 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.103.158] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To kwepemm600005.china.huawei.com (7.193.23.191) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/10/18 20:01, Jason Gunthorpe Wrote: > On Tue, Oct 18, 2022 at 03:06:43PM +0800, liulongfang wrote: >> On 2022/10/17 20:11, Jason Gunthorpe Wrote: >>> On Mon, Oct 17, 2022 at 05:20:34PM +0800, liulongfang wrote: >>>> On 2022/10/14 17:20, John Garry wrote: >>>>> On 14/10/2022 03:57, Longfang Liu wrote: >>>>>> +static void hisi_acc_vf_debugfs_init(struct hisi_acc_vf_core_device *hisi_acc_vdev) >>>>>> +{ >>>>>> +    struct pci_dev *vf_pdev = hisi_acc_vdev->vf_dev; >>>>>> +    struct device *dev = &vf_pdev->dev; >>>>>> +    int ret; >>>>>> + >>>>>> +    if (!atomic_read(&hisi_acc_root_ref)) >>>>>> +        hisi_acc_debugfs_root = debugfs_create_dir("hisi_vfio_acc", NULL); >>>>>> +    atomic_inc(&hisi_acc_root_ref); >>>>>> + >>>>> >>>>> This looks totally racy, such that I wonder why even bother using an atomic for hisi_acc_root_ref. >>>> >>>> >>>> When enabling VF, it is possible for multiple VMs to enable VF at the same time. The atomic variable >>>> is used to ensure that only one "hisi_vfio_acc" is created. When other VFs are enabled, >>>> it will not be created again, but will be used directly. >>> >>> It is still completely racy. Use a lock >>> Um! I understand your previous solution. Since we did not put module_init() in the driver, to avoid competition, we first need to modify the module_init() interface of the driver, then put debugfs_create_dir() into module_init(), and finally put debugfs_create_file() into probe(). I will implement this way in the next version. >> >> Do you have any suggested solutions? > > If you want to keep it like this, use a lock around the creation. > > Jason > . > Thanks, Longfang