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, 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 84482C43333 for ; Thu, 4 Mar 2021 00:21:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4843764E59 for ; Thu, 4 Mar 2021 00:21:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355188AbhCDAUy (ORCPT ); Wed, 3 Mar 2021 19:20:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54160 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1391339AbhCCWfn (ORCPT ); Wed, 3 Mar 2021 17:35:43 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2AABFC061765 for ; Wed, 3 Mar 2021 14:31:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=uxcabn3wqFm81K76yERP5Jq8qLeb2n12aROGe2TGsBo=; b=MqNawF61qndKBCbb8lCH50ToBB 6lGL5GhI1yMODUQz+risarso/AwjpJzk8katuVrqhA2BknvoVezrw3Zo5Q/JQGB6KWHsisxTNOATZ MR2G+qheZNDVCnVOuKzWxjM+r9Px+m9B7BGbp8sGPOyO/VHh8E4IA/otxH4GlUPxOgIXStBIOiQyb vNEtYEffIl9Lg6v+OffgjaQ8TUYLUkHkxM8d8sh+vJMZVpuC+5CMU+g9NVBZq86te1h6GE3L/cem9 yJVGlvktr6w5TuVqxsPCzHxlAcjZdihG3Xpbhbw3NOtfUP4cb5K8IiO2Z91BYVRZLDBx3T3mJ6gLp 7Ek6bopA==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lHa1s-004RGE-GF; Wed, 03 Mar 2021 22:31:41 +0000 Date: Wed, 3 Mar 2021 22:31:40 +0000 From: Matthew Wilcox To: Andrew Morton 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: <20210303223140.GH2723601@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> <20210303135142.e9b71e644958d79ecd3da5b7@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210303135142.e9b71e644958d79ecd3da5b7@linux-foundation.org> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, Mar 03, 2021 at 01:51:42PM -0800, Andrew Morton wrote: > 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? Originally it prevented the opposite race from being misinterpreted; we didn't care if it was truncated after we saw it was Uptodate; we cared if it was !Uptodate because it had been truncated. Now, it's just pointless.