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 EDBB0C64E7D for ; Fri, 20 Nov 2020 09:16:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A274F2224C for ; Fri, 20 Nov 2020 09:16:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727428AbgKTJPx (ORCPT ); Fri, 20 Nov 2020 04:15:53 -0500 Received: from verein.lst.de ([213.95.11.211]:42108 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727354AbgKTJPw (ORCPT ); Fri, 20 Nov 2020 04:15:52 -0500 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) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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.