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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 C07CAC433E0 for ; Thu, 28 Jan 2021 09:32:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7B9FD64DE6 for ; Thu, 28 Jan 2021 09:32:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232437AbhA1Jbb (ORCPT ); Thu, 28 Jan 2021 04:31:31 -0500 Received: from mx2.suse.de ([195.135.220.15]:53970 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232395AbhA1JY2 (ORCPT ); Thu, 28 Jan 2021 04:24:28 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 6CE71AE12; Thu, 28 Jan 2021 09:23:43 +0000 (UTC) Subject: Re: [PATCH v2] nvme-multipath: Early exit if no path is available To: Chao Leng , Daniel Wagner Cc: linux-nvme@lists.infradead.org, Sagi Grimberg , linux-kernel@vger.kernel.org, Jens Axboe , Keith Busch , Christoph Hellwig References: <20210127103033.15318-1-dwagner@suse.de> <20210128075837.u5u56t23fq5gu6ou@beryllium.lan> <69575290-200e-b4a1-4269-c71e4c2cc37b@huawei.com> From: Hannes Reinecke Message-ID: <8704038d-0b71-5c9c-2d2b-a9ff2166dbe4@suse.de> Date: Thu, 28 Jan 2021 10:23:42 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <69575290-200e-b4a1-4269-c71e4c2cc37b@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/28/21 10:18 AM, Chao Leng wrote: > > > On 2021/1/28 15:58, Daniel Wagner wrote: >> On Thu, Jan 28, 2021 at 09:31:30AM +0800, Chao Leng wrote: >>>> --- a/drivers/nvme/host/multipath.c >>>> +++ b/drivers/nvme/host/multipath.c >>>> @@ -221,7 +221,7 @@ static struct nvme_ns >>>> *nvme_round_robin_path(struct nvme_ns_head *head, >>>>        } >>>>        for (ns = nvme_next_ns(head, old); >>>> -         ns != old; >>>> +         ns && ns != old; >>> nvme_round_robin_path just be called when !"old". >>> nvme_next_ns should not return NULL when !"old". >>> It seems unnecessary to add checking "ns". >> >> The problem is when we enter nvme_round_robin_path() and there is no >> path available. In this case the initialization ns = nvme_next_ns(head, >> old) could return a NULL pointer."old" should not be NULL, so there is >> at least one path that is "old". > It is impossible to return NULL for nvme_next_ns(head, old). No. list_next_or_null_rcu()/list_first_or_null_rcu() will return NULL when then end of the list is reached. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer