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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 7632AC433DB for ; Tue, 5 Jan 2021 21:35:07 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id F355022D6E for ; Tue, 5 Jan 2021 21:35:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F355022D6E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 439116B00FC; Tue, 5 Jan 2021 16:35:06 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 3E8956B00FF; Tue, 5 Jan 2021 16:35:06 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2FE4F6B0100; Tue, 5 Jan 2021 16:35:06 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0159.hostedemail.com [216.40.44.159]) by kanga.kvack.org (Postfix) with ESMTP id 1C6D16B00FC for ; Tue, 5 Jan 2021 16:35:06 -0500 (EST) Received: from smtpin18.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id CCD44362D for ; Tue, 5 Jan 2021 21:35:05 +0000 (UTC) X-FDA: 77673026970.18.aunt80_4901cc8274dc Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin18.hostedemail.com (Postfix) with ESMTP id 7F015100EC66D for ; Tue, 5 Jan 2021 21:35:05 +0000 (UTC) X-HE-Tag: aunt80_4901cc8274dc X-Filterd-Recvd-Size: 3403 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf43.hostedemail.com (Postfix) with ESMTP for ; Tue, 5 Jan 2021 21:35:04 +0000 (UTC) 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=4fXXGhqhwyZOyY/MzNL+cRERt9hfQzFKJ23KP07oxrg=; b=PMmrvrHj+uqoxe55GQq/rvMKul vnT6PdTMKIcWp7KrN5DXA+ZEJiz3CBALxwj1Uqo8nFC1NGwaoyQK3Grlyl79zD5LUpt+4czdLxlL5 2cFEeUZZwnxF78MglNWKES4nrdE+4r9hJ5R1kL+wG/6X9hXK474xKhoyFxg7D1uU8MqOh43ksyJKo pt+S0Vvu7wC+71IE0zC5Cjr7ZiWiLMcxNh1JE65auWFmVWs8sn/AVPG2ByO8YbpGMC92YxQdplu46 h/1uASJyw59tHRhBS60tWeXSpBra+QkpGB8Fla2VFDBn/JzRJajbg7BlYVZ3xch6t6BGg+TbOCOvo dSjnFwNQ==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1kwtyL-001hQZ-DD; Tue, 05 Jan 2021 21:34:42 +0000 Date: Tue, 5 Jan 2021 21:34:33 +0000 From: Matthew Wilcox To: Linus Torvalds Cc: Hugh Dickins , Andrew Morton , syzbot , Linux Kernel Mailing List , Linux-MM , syzkaller-bugs Subject: Re: kernel BUG at mm/page-writeback.c:LINE! Message-ID: <20210105213433.GC175893@casper.infradead.org> References: <000000000000886dbd05b7ffa8db@google.com> <20210104124153.0992b1f7fd1a145e193a333f@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Tue, Jan 05, 2021 at 01:22:49PM -0800, Linus Torvalds wrote: > On Tue, Jan 5, 2021 at 1:13 PM Hugh Dickins wrote: > > > > I was going to raise a question, whether you should now revert > > 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and BUG_ON(PageWriteback)"): > > which would not have gone in like that if c2407cf7d22d were already in. > > Honestly, even if it wasn't for that PageTail issue, I think > 073861ed77b6 is just the right thing to do anyway. It just feels _so_ > much safer to not have the possibility of that page wait thing > following while the page is possibly then being free'd and re-used at > the same time. > > So I think the only reason to revert that commit would be if we were > to find that it's a huge performance problem to raise the page > refcount temporarily. Which I think is very unlikely (since we already > dirty the page structure due to the page flags modification - although > they are far enough apart that it might be a different cacheline). struct pages _tend_ to be 64 bytes on 64-bit platforms (and i suspect you're long past caring about performance on 32-bit platforms).