From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-fsdevel-owner@kernel.org>
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 0D0FEC2D0E4
	for <linux-fsdevel@archiver.kernel.org>; Fri, 20 Nov 2020 15:33:22 +0000 (UTC)
Received: from vger.kernel.org (vger.kernel.org [23.128.96.18])
	by mail.kernel.org (Postfix) with ESMTP id BE7A8238E6
	for <linux-fsdevel@archiver.kernel.org>; Fri, 20 Nov 2020 15:33:21 +0000 (UTC)
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1729828AbgKTPc7 (ORCPT
        <rfc822;linux-fsdevel@archiver.kernel.org>);
        Fri, 20 Nov 2020 10:32:59 -0500
Received: from verein.lst.de ([213.95.11.211]:43415 "EHLO verein.lst.de"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1728264AbgKTPc6 (ORCPT <rfc822;linux-fsdevel@vger.kernel.org>);
        Fri, 20 Nov 2020 10:32:58 -0500
Received: by verein.lst.de (Postfix, from userid 2407)
        id ED47B67373; Fri, 20 Nov 2020 16:32:53 +0100 (CET)
Date:   Fri, 20 Nov 2020 16:32:53 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Jan Kara <jack@suse.cz>
Cc:     Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        Tejun Heo <tj@kernel.org>, Josef Bacik <josef@toxicpanda.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Coly Li <colyli@suse.de>, Mike Snitzer <snitzer@redhat.com>,
        dm-devel@redhat.com, Richard Weinberger <richard@nod.at>,
        Jan Kara <jack@suse.com>, 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 14/20] block: remove the nr_sects field in struct
 hd_struct
Message-ID: <20201120153253.GA18990@lst.de>
References: <20201118084800.2339180-1-hch@lst.de> <20201118084800.2339180-15-hch@lst.de> <20201119120525.GW1981@quack2.suse.cz> <20201120090820.GD21715@lst.de> <20201120112121.GB15537@quack2.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20201120112121.GB15537@quack2.suse.cz>
User-Agent: Mutt/1.5.17 (2007-11-01)
Precedence: bulk
List-ID: <linux-fsdevel.vger.kernel.org>
X-Mailing-List: linux-fsdevel@vger.kernel.org

On Fri, Nov 20, 2020 at 12:21:21PM +0100, Jan Kara wrote:
> > > AFAICT bd_size_lock is pointless after these changes so we can just remove
> > > it?
> > 
> > I don't think it is, as reuqiring bd_mutex for size updates leads to
> > rather awkward lock ordering problems.
> 
> OK, let me ask differently: What is bd_size_lock protecting now? Ah, I see,
> on 32-bit it is needed to prevent torn writes to i_size, right?

Exactly.  In theory we could skip it for 64-bit, but as updating the
size isn't a fast path, and struct block_device isn't super size critical
I'd rather keep the same code for 32 vs 64-bit builds.