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,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 D6649C63777 for ; Fri, 20 Nov 2020 09:15:53 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 21CB02224C for ; Fri, 20 Nov 2020 09:15:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 21CB02224C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 944466B006C; Fri, 20 Nov 2020 04:15:52 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 91BA96B0070; Fri, 20 Nov 2020 04:15:52 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 835036B0072; Fri, 20 Nov 2020 04:15:52 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0131.hostedemail.com [216.40.44.131]) by kanga.kvack.org (Postfix) with ESMTP id 4C4636B006C for ; Fri, 20 Nov 2020 04:15:52 -0500 (EST) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id E2079362E for ; Fri, 20 Nov 2020 09:15:51 +0000 (UTC) X-FDA: 77504239302.02.push44_57020af2734a Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin02.hostedemail.com (Postfix) with ESMTP id C9C3210097AA0 for ; Fri, 20 Nov 2020 09:15:51 +0000 (UTC) X-HE-Tag: push44_57020af2734a X-Filterd-Recvd-Size: 3287 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by imf48.hostedemail.com (Postfix) with ESMTP for ; Fri, 20 Nov 2020 09:15:51 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id 8D37C67373; Fri, 20 Nov 2020 10:15:47 +0100 (CET) Date: Fri, 20 Nov 2020 10:15:46 +0100 From: Christoph Hellwig To: Jan Kara Cc: Christoph Hellwig , Jens Axboe , Tejun Heo , Josef Bacik , Konrad Rzeszutek Wilk , Coly Li , Mike Snitzer , dm-devel@redhat.com, Richard Weinberger , Jan Kara , linux-block@vger.kernel.org, xen-devel@lists.xenproject.org, linux-bcache@vger.kernel.org, linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 15/20] block: merge struct block_device and struct hd_struct Message-ID: <20201120091546.GE21715@lst.de> References: <20201118084800.2339180-1-hch@lst.de> <20201118084800.2339180-16-hch@lst.de> <20201119143921.GX1981@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201119143921.GX1981@quack2.suse.cz> User-Agent: Mutt/1.5.17 (2007-11-01) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Nov 19, 2020 at 03:39:21PM +0100, Jan Kara wrote: > This patch is kind of difficult to review due to the size of mostly > mechanical changes mixed with not completely mechanical changes. Can we > perhaps split out the mechanical bits? E.g. the rq->part => rq->bdev > renaming is mechanical and notable part of the patch. Similarly the > part->foo => part->bd_foo bits... We'd end with really weird patches that way. Never mind that I'm not even sure how we could mechnically do the renaming. > > Also I'm kind of wondering: AFAIU the new lifetime rules, gendisk holds > bdev reference and bdev is created on gendisk allocation so bdev lifetime is > strictly larger than gendisk lifetime. But what now keeps bdev->bd_disk > reference safe in presence device hot unplug? In most cases we are still > protected by gendisk reference taken in __blkdev_get() but how about > disk->lookup_sem and disk->flags dereferences before we actually grab the > reference? Good question. I'll need to think about this a bit more. > Also I find it rather non-obvious (although elegant ;) that bdev->bd_device > rules the lifetime of gendisk. Can you perhaps explain this in the > changelog and probably also add somewhere to source a documentation about > the new lifetime rules? Yes. > > -struct hd_struct *__disk_get_part(struct gendisk *disk, int partno); > > +static inline struct block_device *__bdget_disk(struct gendisk *disk, > > + int partno) > > +{ > > + struct disk_part_tbl *ptbl = rcu_dereference(disk->part_tbl); > > + > > + if (unlikely(partno < 0 || partno >= ptbl->len)) > > + return NULL; > > + return rcu_dereference(ptbl->part[partno]); > > +} > > I understand this is lower-level counterpart of bdget_disk() but it is > confusing to me that this has 'bdget' in the name and returns no bdev > reference. Can we call it like __bdev_from_disk() or something like that? Sure.