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 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 F1C2BC433DB for ; Tue, 5 Jan 2021 21:35:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BCBC722D6E for ; Tue, 5 Jan 2021 21:35:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731487AbhAEVfm (ORCPT ); Tue, 5 Jan 2021 16:35:42 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39012 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725817AbhAEVfl (ORCPT ); Tue, 5 Jan 2021 16:35:41 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 44C5AC061574 for ; Tue, 5 Jan 2021 13:35:01 -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=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: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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).