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 B5535C04A95 for ; Tue, 25 Oct 2022 09:15:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232164AbiJYJPq (ORCPT ); Tue, 25 Oct 2022 05:15:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48826 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232346AbiJYJPX (ORCPT ); Tue, 25 Oct 2022 05:15:23 -0400 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1C85E17D851; Tue, 25 Oct 2022 02:08:16 -0700 (PDT) Received: from frapeml100006.china.huawei.com (unknown [172.18.147.200]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4MxQzJ61yrz67bjw; Tue, 25 Oct 2022 17:06:20 +0800 (CST) Received: from lhrpeml500003.china.huawei.com (7.191.162.67) by frapeml100006.china.huawei.com (7.182.85.201) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Tue, 25 Oct 2022 11:08:13 +0200 Received: from [10.195.245.7] (10.195.245.7) by lhrpeml500003.china.huawei.com (7.191.162.67) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Tue, 25 Oct 2022 10:08:12 +0100 Message-ID: Date: Tue, 25 Oct 2022 10:08:10 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: [PATCH] blk-mq: Properly init bios from blk_mq_alloc_request_hctx() To: Ming Lei CC: , , , , Bart Van Assche References: <1666454846-11749-1-git-send-email-john.garry@huawei.com> <99c6ca81-746d-85f4-04d3-49d7a3de611b@huawei.com> <360c78dc-65ce-362f-389d-075f2259ce5b@huawei.com> <3513b14c-14e0-b865-628e-a83521090de9@huawei.com> From: John Garry In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.195.245.7] X-ClientProxiedBy: lhrpeml500003.china.huawei.com (7.191.162.67) To lhrpeml500003.china.huawei.com (7.191.162.67) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 25/10/2022 10:00, Ming Lei wrote: >> My use case is in SCSI EH domain. For my HBA controller of interest, to >> abort an erroneous IO we must send a controller proprietary abort >> command on same HW queue as original command. So we would need to >> allocate this abort request for a specific HW queue. > IMO, it is one bad hw/sw interface. > > First such request has to be reserved, since all inflight IOs can be in error. Right > > Second error handling needs to provide forward-progress, and it is supposed > to not require external dependency, otherwise easy to cause deadlock, but > here request from specific HW queue just depends on this queue's cpumask. > > Also if it has to be reserved, it can be done as one device/driver private > command, so why bother blk-mq for this special use case? I have a series for reserved request support, which I will send later. Please have a look. And as I mentioned, I would prob not end up using blk_mq_alloc_request_hctx() anyway. > >> I mentioned before that if no hctx->cpumask is online then we don't need >> to allocate a request. That is because if no hctx->cpumask is online, >> this means that original erroneous IO must be completed due to nature of >> how blk-mq cpu hotplug handler works, i.e. drained, and then we don't >> actually need to abort it any longer, so ok to not get a request. > No, it is really not OK, if all cpus in hctx->cpumask are offline, you > can't allocate > request on the specified hw queue, then the erroneous IO can't be handled, > then cpu hotplug handler may hang for ever. If the erroneous IO is still in-flight from blk-mq perspective, then how can hctx->cpumask still be offline? I thought that we guarantee that hctx->cpumask cannot go offline until drained. Thanks, John