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 86B51C38A2D for ; Tue, 25 Oct 2022 09:32:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230388AbiJYJch (ORCPT ); Tue, 25 Oct 2022 05:32:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60244 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229763AbiJYJcg (ORCPT ); Tue, 25 Oct 2022 05:32:36 -0400 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 166F4EC504; Tue, 25 Oct 2022 02:32:33 -0700 (PDT) Received: from frapeml500005.china.huawei.com (unknown [172.18.147.200]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4MxRWy46CWz687w5; Tue, 25 Oct 2022 17:31:10 +0800 (CST) Received: from lhrpeml500003.china.huawei.com (7.191.162.67) by frapeml500005.china.huawei.com (7.182.85.13) 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 11:32:31 +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 10:32:30 +0100 Message-ID: <399a2c2d-0b56-e4e7-c309-a6b9537d8939@huawei.com> Date: Tue, 25 Oct 2022 10:32:28 +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: lhrpeml100006.china.huawei.com (7.191.160.224) 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 10:16, Ming Lei wrote: >>>> 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. > Yeah, the draining is done before the cpu is offline. But the drain is > simply waiting for the inflight IO to be completed. If the IO is failed > during the waiting, you can't allocate such reserved request for error > handling, then hang ever in blk_mq_hctx_notify_offline(). Actually if final cpu in hctx->cpumask is going offline, then hctx won't queue any more requests, right? In this case I don't think we can queue on that hctx anyway. I need to think about this more. > > If you just make it one driver private command, there can't be such > issue. Well we're trying to use reserved requests for EH commands, which that goes against. > Block layer is supposed for handling common case(normal io and pt io), > I'd suggest to not put such special cases into block layer. It also supports reserved commands, which I would assume would be suitable for EH scenarios. Thanks, John