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=-5.2 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 33B61C56202 for ; Thu, 26 Nov 2020 18:22:24 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6BC2A20B80 for ; Thu, 26 Nov 2020 18:22:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6BC2A20B80 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 83E186B005D; Thu, 26 Nov 2020 13:22:22 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7ED316B0070; Thu, 26 Nov 2020 13:22:22 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6DC1B6B0072; Thu, 26 Nov 2020 13:22:22 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0114.hostedemail.com [216.40.44.114]) by kanga.kvack.org (Postfix) with ESMTP id 59A596B005D for ; Thu, 26 Nov 2020 13:22:22 -0500 (EST) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 1F26E3640 for ; Thu, 26 Nov 2020 18:22:22 +0000 (UTC) X-FDA: 77527389324.08.smile72_450a25127381 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin08.hostedemail.com (Postfix) with ESMTP id 007C61819E766 for ; Thu, 26 Nov 2020 18:22:21 +0000 (UTC) X-HE-Tag: smile72_450a25127381 X-Filterd-Recvd-Size: 2546 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf07.hostedemail.com (Postfix) with ESMTP for ; Thu, 26 Nov 2020 18:22:21 +0000 (UTC) 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 4F7B7AF27; Thu, 26 Nov 2020 18:22:20 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 8EEA81E10D0; Thu, 26 Nov 2020 19:22:19 +0100 (CET) Date: Thu, 26 Nov 2020 19:22:19 +0100 From: Jan Kara To: Christoph Hellwig Cc: Jens Axboe , Tejun Heo , Josef Bacik , Coly Li , Mike Snitzer , Greg Kroah-Hartman , Jan Kara , Johannes Thumshirn , dm-devel@redhat.com, Jan Kara , linux-block@vger.kernel.org, linux-bcache@vger.kernel.org, linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Chao Yu Subject: Re: [PATCH 37/44] block: switch partition lookup to use struct block_device Message-ID: <20201126182219.GC422@quack2.suse.cz> References: <20201126130422.92945-1-hch@lst.de> <20201126130422.92945-38-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201126130422.92945-38-hch@lst.de> User-Agent: Mutt/1.10.1 (2018-07-13) 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 26-11-20 14:04:15, Christoph Hellwig wrote: > struct hd_struct *disk_get_part(struct gendisk *disk, int partno) > { > - struct hd_struct *part; > + struct block_device *part; > > rcu_read_lock(); > part = __disk_get_part(disk, partno); > - if (part) > - get_device(part_to_dev(part)); > - rcu_read_unlock(); > + if (!part) { > + rcu_read_unlock(); > + return NULL; > + } > > - return part; > + get_device(part_to_dev(part->bd_part)); > + rcu_read_unlock(); > + return part->bd_part; > } This is not directly related to this particular patch but I'm wondering: What prevents say del_gendisk() from racing with disk_get_part(), so that delete_partition() is called just after we fetched 'part' pointer and the last 'part' kobject ref is dropped before disk_get_part() calls get_device()? I don't see anything preventing that and so we'd hand out 'part' that is soon to be freed (after RCU grace period expires). Honza -- Jan Kara SUSE Labs, CR