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=-6.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 3BE0AC2B9F4 for ; Fri, 25 Jun 2021 13:00:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 23E8A61465 for ; Fri, 25 Jun 2021 13:00:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231659AbhFYNDC (ORCPT ); Fri, 25 Jun 2021 09:03:02 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:59553 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231386AbhFYNDB (ORCPT ); Fri, 25 Jun 2021 09:03:01 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1624626040; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=B3OQ+6kMWXEqLkzrnVZadaNPJSKIMvnSIu0r7ijAo9w=; b=AdaaYg2E8MlOmtNBZjQH3xNxu2GxaacwA6FPN/SaYyLXZqwdXxUEGn+UN7CnmZYQQQmZU0 JaP7ITnuzuf4SXFrHn5X3gPIPkkCFjmoijJGvYTnY70iJjii6ZkVO3QmTkpg2JFF5Cak8m eSOVybXreJGlKdgZB8etzP+5S0LG6dY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-512-17j0dxvzNJCKsipDIIqaXw-1; Fri, 25 Jun 2021 09:00:38 -0400 X-MC-Unique: 17j0dxvzNJCKsipDIIqaXw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2D44A802C92; Fri, 25 Jun 2021 13:00:37 +0000 (UTC) Received: from T590 (ovpn-12-153.pek2.redhat.com [10.72.12.153]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D3D09136F5; Fri, 25 Jun 2021 13:00:29 +0000 (UTC) Date: Fri, 25 Jun 2021 21:00:25 +0800 From: Ming Lei To: Daniel Wagner Cc: linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, James Smart , Keith Busch , Jens Axboe , Sagi Grimberg Subject: Re: [PATCH 0/2] Handle update hardware queues and queue freeze more carefully Message-ID: References: <20210625101649.49296-1-dwagner@suse.de> <20210625122156.x5yzoobuaaec5hss@beryllium.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210625122156.x5yzoobuaaec5hss@beryllium.lan> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 25, 2021 at 02:21:56PM +0200, Daniel Wagner wrote: > On Fri, Jun 25, 2021 at 12:16:47PM +0200, Daniel Wagner wrote: > > this is a followup on the crash I reported in > > > > https://lore.kernel.org/linux-block/20210608183339.70609-1-dwagner@suse.de/ > > > > By moving the hardware check up the crash was gone. Unfortuntatly, I > > don't understand why this fixes the crash. The per-cpu access is > > crashing but I can't see why the blk_mq_update_nr_hw_queues() is > > fixing this problem. > > > > Even though I can't explain why it fixes it, I think it makes sense to > > update the hardware queue mapping bevore we recreate the IO > > queues. Thus I avoided in the commit message to say it fixes > > something. > > I just discussed this with Hannes and we figured out how the crash is > fixed by moving the blk_mq_update_nr_hw_queues() before the > nvme_fc_create_hw_io_queues()/nvme_fc_connect_io_queues(). > > First of all, blk_mq_update_nr_hw_queues() operates on the normal > tag_set and not the admin_tag_set. That means when we move the > blk_mq_update_nr_hw_queues() before the nvme_fc_connect_io_queues(), we > update the mapping to only CPUs and hwctx which are available. When we > then do the connect call nvmf_connect_io_queue() we will only allocate > tags from queues which are not in the BLK_MQ_S_INACTIVE anymore. Hence > we skip the blk_mq_put_tag() call. Your patch just reduces the race window, what if all cpus in hctx->cpumask become offline when calling blk_mq_alloc_request_hctx()? Thanks, Ming