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 46830C63777 for ; Thu, 3 Dec 2020 09:27:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DA92E217A0 for ; Thu, 3 Dec 2020 09:27:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726627AbgLCJ1M (ORCPT ); Thu, 3 Dec 2020 04:27:12 -0500 Received: from frasgout.his.huawei.com ([185.176.79.56]:2197 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387479AbgLCJ1L (ORCPT ); Thu, 3 Dec 2020 04:27:11 -0500 Received: from fraeml703-chm.china.huawei.com (unknown [172.18.147.226]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4Cmr5D6xLDz67LZT; Thu, 3 Dec 2020 17:24:32 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml703-chm.china.huawei.com (10.206.15.52) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2106.2; Thu, 3 Dec 2020 10:26:29 +0100 Received: from [10.47.8.200] (10.47.8.200) 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 15.1.1913.5; Thu, 3 Dec 2020 09:26:28 +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> From: John Garry Message-ID: Date: Thu, 3 Dec 2020 09:26:00 +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: <20201203005505.GB540033@T590> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.47.8.200] X-ClientProxiedBy: lhreml734-chm.china.huawei.com (10.201.108.85) 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 On 03/12/2020 00:55, Ming Lei wrote: Hi Ming, >> Yeah, so I said that was another problem which you mentioned there, which >> I'm not addressing, but I don't think that I'm making thing worse here. > The thing is that this patch does not fix the issue completely. > >> So AFAICS, the blk-mq/sched code doesn't wait for any "readers" to be >> finished, such as those running blk_mq_queue_tag_busy_iter or >> blk_mq_tagset_busy_iter() in another context. >> >> So how about the idea of introducing some synchronization primitive, such as >> semaphore, which those "readers" must grab and release at start and end (of >> iter), to ensure the requests are not freed during the iteration? > It looks good, however devil is in details, please make into patch for > review. OK, but another thing to say is that I need to find a somewhat reliable reproducer for the potential problem you mention. So far this patch solves the issue I see (in that kasan stops warning). Let me analyze this a bit further. Thanks, John