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 CA2D8C433FE for ; Tue, 18 Oct 2022 07:06:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229610AbiJRHGv (ORCPT ); Tue, 18 Oct 2022 03:06:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52764 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229732AbiJRHGr (ORCPT ); Tue, 18 Oct 2022 03:06:47 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6F18FA8CFD for ; Tue, 18 Oct 2022 00:06:46 -0700 (PDT) Received: from dggemv703-chm.china.huawei.com (unknown [172.30.72.55]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4Ms4bV3bPdzJn7H; Tue, 18 Oct 2022 15:04:06 +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; Tue, 18 Oct 2022 15:06:44 +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; Tue, 18 Oct 2022 15:06:43 +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> From: liulongfang Message-ID: <9826a418-4a14-aa4a-9eb8-6faf3e43c8e3@huawei.com> Date: Tue, 18 Oct 2022 15:06:43 +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: dggems706-chm.china.huawei.com (10.3.19.183) 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 2022/10/17 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 > Do you have any suggested solutions? > Jason > . > Thanks, Longfang