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 E9645C54EBC for ; Thu, 12 Jan 2023 06:18:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236805AbjALGS1 (ORCPT ); Thu, 12 Jan 2023 01:18:27 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36056 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236566AbjALGSX (ORCPT ); Thu, 12 Jan 2023 01:18:23 -0500 Received: from dggsgout11.his.huawei.com (unknown [45.249.212.51]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 96D931263E; Wed, 11 Jan 2023 22:18:22 -0800 (PST) Received: from mail02.huawei.com (unknown [172.30.67.153]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4NsvVv0tWQz4f3wQw; Thu, 12 Jan 2023 14:18:15 +0800 (CST) Received: from [10.174.176.73] (unknown [10.174.176.73]) by APP1 (Coremail) with SMTP id cCh0CgCXtjAnpr9jeF7hBQ--.43940S3; Thu, 12 Jan 2023 14:18:17 +0800 (CST) Subject: Re: [PATCH v2 1/2] blk-iocost: add refcounting for iocg To: Tejun Heo , Yu Kuai Cc: hch@infradead.org, josef@toxicpanda.com, axboe@kernel.dk, cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, yi.zhang@huawei.com, "yukuai (C)" References: <7dcdaef3-65c1-8175-fea7-53076f39697f@huaweicloud.com> <875eb43e-202d-5b81-0bff-ef0434358d99@huaweicloud.com> <53b30ac8-d608-ba0b-8b1b-7fe5cfed6d61@huaweicloud.com> From: Yu Kuai Message-ID: <4aeef320-c6c8-d9b4-8826-d58f00ea6264@huaweicloud.com> Date: Thu, 12 Jan 2023 14:18:15 +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; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID: cCh0CgCXtjAnpr9jeF7hBQ--.43940S3 X-Coremail-Antispam: 1UD129KBjvJXoW7CF15Aw4UGr1kXr1kZryxZrb_yoW8GFW8pF WfG3sagrWvyw1IyrnFyw4xX34Ska1UAr15KFyDG3yfCr4Fgr92kFyfAr1DAF93JFs5tFyY gFyYgF17W39rAF7anT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUU9Y14x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26F1j6w1UM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4U JVWxJr1l84ACjcxK6I8E87Iv67AKxVW0oVCq3wA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_Gc CE3s1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx0E 2Ix0cI8IcVAFwI0_Jr0_Jr4lYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE7xkEbVWUJV W8JwACjcxG0xvEwIxGrwACjI8F5VA0II8E6IAqYI8I648v4I1lFIxGxcIEc7CjxVA2Y2ka 0xkIwI1lc7I2V7IY0VAS07AlzVAYIcxG8wCF04k20xvY0x0EwIxGrwCFx2IqxVCFs4IE7x kEbVWUJVW8JwC20s026c02F40E14v26r1j6r18MI8I3I0E7480Y4vE14v26r106r1rMI8E 67AF67kF1VAFwI0_Jw0_GFylIxkGc2Ij64vIr41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCw CI42IY6xIIjxv20xvEc7CjxVAFwI0_Jr0_Gr1lIxAIcVCF04k26cxKx2IYs7xG6rW3Jr0E 3s1lIxAIcVC2z280aVAFwI0_Jr0_Gr1lIxAIcVC2z280aVCY1x0267AKxVWUJVW8JbIYCT nIWIevJa73UjIFyTuYvjfUoOJ5UUUUU X-CM-SenderInfo: 51xn3trlr6x35dzhxuhorxvhhfrp/ X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, 在 2023/01/12 1:07, Tejun Heo 写道: > Hello, > > On Wed, Jan 11, 2023 at 09:36:25AM +0800, Yu Kuai wrote: >> I'm not sure, of course this can fix the problem, but two spinlock >> 'blkcg->lock' and 'q->queue_lock' are used to protect blkg_destroy() >> currently, add a mutex（disk level?) requires a refactor, which seems >> complex to me. > > The fact that the two paths can race each other already seems buggy. e.g. > What prevents them from running pd_free on the same pd twice? So, it needs I think the root cause is that blkg is tracked from two different list, blkcg->blkg_list from cgroup level and q->blkg_list from disk level. And pd_free_fn is also called from both blkg_destroy() and deactivate policy for a disk. I just thought about another solution: remove the blkcg_deactivate_policy() from rq_qos_exit() from deleting the device, and delay the policy cleanup and free to blkg_destroy_all(). Then the policies(other than bfq) can only call pd_free_fn() from blkg_destroy(), and it's easy to guarantee the order. For bfq, it can stay the same since bfq has refcounting itself. Then for the problem that ioc can be freed in pd_free_fn(), we can fix it by freeing ioc in ioc_pd_free() for root blkg instead of rq_qos_exit(). What do you think? Thanks, Kuai > to be fixed anyway and the intention always has been that these callbacks > are called in the correct traversal order. > > Thanks. >