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 31346C4361B for ; Thu, 10 Dec 2020 10:46:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EC99923D6A for ; Thu, 10 Dec 2020 10:46:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388932AbgLJKqN (ORCPT ); Thu, 10 Dec 2020 05:46:13 -0500 Received: from frasgout.his.huawei.com ([185.176.79.56]:2240 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731564AbgLJKqM (ORCPT ); Thu, 10 Dec 2020 05:46:12 -0500 Received: from fraeml740-chm.china.huawei.com (unknown [172.18.147.207]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4Cs9Vy2vsTz67Cr2; Thu, 10 Dec 2020 18:43:22 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml740-chm.china.huawei.com (10.206.15.221) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2106.2; Thu, 10 Dec 2020 11:45:29 +0100 Received: from [10.210.172.228] (10.210.172.228) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2106.2; Thu, 10 Dec 2020 10:45:28 +0000 Subject: Re: [RFC PATCH] blk-mq: Clean up references when freeing rqs To: Ming Lei CC: , , , , , , , References: <1606827738-238646-1-git-send-email-john.garry@huawei.com> <20201202033134.GD494805@T590> <20201203005505.GB540033@T590> <7beb86a2-5c4b-bdc0-9fce-1b583548c6d0@huawei.com> <20201209010102.GA1217988@T590> <13327a68-6f86-96da-0c5f-5fa0be326d6f@huawei.com> <20201210020745.GA1363446@T590> From: John Garry Message-ID: Date: Thu, 10 Dec 2020 10:44:54 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.1.2 MIME-Version: 1.0 In-Reply-To: <20201210020745.GA1363446@T590> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.210.172.228] X-ClientProxiedBy: lhreml729-chm.china.huawei.com (10.201.108.80) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Hi Ming, On 10/12/2020 02:07, Ming Lei wrote: >> Apart from this, my concern is that we come with for a solution, but it's a >> complicated solution and may not be accepted as this issue is not seen as a >> problem in practice. > If that is the case, I'd suggest to consider the solution in the > following link: > > https://lore.kernel.org/linux-block/20200820180335.3109216-1-ming.lei@redhat.com/ > > At least, the idea is simple, which can be extended to support allocate driver tags > request pool dynamically. As I see with your approach, we may still iterate a stale request, but it just has not been freed, so just no use-after-free BUG, right? Rather it is cached until all references dropped. It may be best solution. So I'll try an experiment today to prove your concern about blk_mq_queue_tag_busy_iter(). Then look at possible solution which builds on patch in $subject, and compare. Thanks, John