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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 DB189C433E0 for ; Wed, 3 Mar 2021 21:52:02 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3C26364E2E for ; Wed, 3 Mar 2021 21:52:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3C26364E2E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9F1DA6B0005; Wed, 3 Mar 2021 16:52:01 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 9A1F16B0006; Wed, 3 Mar 2021 16:52:01 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 843036B0007; Wed, 3 Mar 2021 16:52:01 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0023.hostedemail.com [216.40.44.23]) by kanga.kvack.org (Postfix) with ESMTP id 65CDD6B0005 for ; Wed, 3 Mar 2021 16:52:01 -0500 (EST) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 16402940D for ; Wed, 3 Mar 2021 21:52:01 +0000 (UTC) X-FDA: 77879911242.29.A588EDC Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf20.hostedemail.com (Postfix) with ESMTP id 16EDF23A2 for ; Wed, 3 Mar 2021 21:51:49 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 1ACE764E51; Wed, 3 Mar 2021 21:51:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1614808303; bh=Uyjfe315JTKU+P74eYYzQCeeoh96/Ueo/u0rRsYK5fU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=qNHiOwQvxzJRdVFS7POywUB45PeTiY7XPDrlENSfHAmPfF4I/vW/SwSW8yinqXhtI UVWW7DPu/7vvLp0iVZT1rwD6Somrix9a+WjQZuE2h54YQmP9jzM3SkDP+E3/TwGCDl T6Lo0UBJaffK3iNM3ZbLL1FlHBC3eIqPlvzX1nCc= Date: Wed, 3 Mar 2021 13:51:42 -0800 From: Andrew Morton To: Matthew Wilcox Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Kent Overstreet , Christoph Hellwig Subject: Re: [PATCH] mm/filemap: Use filemap_read_page in filemap_fault Message-Id: <20210303135142.e9b71e644958d79ecd3da5b7@linux-foundation.org> In-Reply-To: <20210303205736.GG2723601@casper.infradead.org> References: <20210226140011.2883498-1-willy@infradead.org> <20210302173039.4625f403846abd20413f6dad@linux-foundation.org> <20210303013313.GZ2723601@casper.infradead.org> <20210302220735.1f150f28323f676d2955ab49@linux-foundation.org> <20210303132640.GB2723601@casper.infradead.org> <20210303121253.9f44d8129f148b1e2e78cc81@linux-foundation.org> <20210303205736.GG2723601@casper.infradead.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: 5gzc1scn8sbq8tshdgssyi98zzesj58o X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 16EDF23A2 Received-SPF: none (linux-foundation.org>: No applicable sender policy available) receiver=imf20; identity=mailfrom; envelope-from=""; helo=mail.kernel.org; client-ip=198.145.29.99 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614808309-859036 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 Wed, 3 Mar 2021 20:57:36 +0000 Matthew Wilcox wrote: > On Wed, Mar 03, 2021 at 12:12:53PM -0800, Andrew Morton wrote: > > On Wed, 3 Mar 2021 13:26:40 +0000 Matthew Wilcox wrote: > > > > > But here's the thing ... invalidate_mapping_pages() doesn't > > > ClearPageUptodate. The only places where we ClearPageUptodate is on an > > > I/O error. > > > > yup. > > > > > So ... as far as I can tell, the only way to hit this is: > > > > > > - Get an I/O error during the wait > > > - Have another thread cause the page to be removed from the page cache > > > (eg do direct I/O to the file) before this thread is run. > > > > > > and the consequence to this change is that we have another attempt to > > > read the page instead of returning an error immediately. I'm OK with > > > that unintentional change, although I think the previous behaviour was > > > also perfectly acceptable (after all, there was an I/O error while trying > > > to read this page). > > > > > > Delving into the linux-fullhistory tree, this code was introduced by ... > > > > > > commit 56f0d5fe6851037214a041a5cb4fc66199256544 > > > Author: Andrew Morton > > > Date: Fri Jan 7 22:03:01 2005 -0800 > > > > > > [PATCH] readpage-vs-invalidate fix > > > > > > A while ago we merged a patch which tried to solve a problem wherein a > > > concurrent read() and invalidate_inode_pages() would cause the read() to > > > return -EIO because invalidate cleared PageUptodate() at the wrong time. > > > > > > We no longer clear PageUptodate, so I think this is stale code? Perhaps > > > you could check with the original author ... > > > > Which code do you think might be stale? We need the !PageUptodate > > check to catch IO errors and we need the !page->mapping check to catch > > invalidates. Am a bit confused. > > I think the check of !page->mapping here: > > if (PageUptodate(page)) > return 0; > if (!page->mapping) /* page truncated */ > return AOP_TRUNCATED_PAGE; > > is no longer needed. If we didn't see an error, the page will be Uptodate, > regardless of whether it's been removed from the page cache. If we did > see an error, it's OK to return -EIO, even if the page has been removed > from the page cache in the interim. OK. Checking page->mapping of an unlocked page seems meaningless anyway - what's to prevent it from being truncated just after we checked?