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=-15.1 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1, USER_IN_DEF_DKIM_WL 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 B4D53C433E0 for ; Tue, 5 Jan 2021 21:14:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8230F22D5A for ; Tue, 5 Jan 2021 21:14:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730634AbhAEVOd (ORCPT ); Tue, 5 Jan 2021 16:14:33 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35714 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725940AbhAEVOd (ORCPT ); Tue, 5 Jan 2021 16:14:33 -0500 Received: from mail-ot1-x334.google.com (mail-ot1-x334.google.com [IPv6:2607:f8b0:4864:20::334]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 16668C061574 for ; Tue, 5 Jan 2021 13:13:53 -0800 (PST) Received: by mail-ot1-x334.google.com with SMTP id b24so1134348otj.0 for ; Tue, 05 Jan 2021 13:13:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:in-reply-to:message-id:references :user-agent:mime-version; bh=TyYwTxr/bbnMT2s7IdFCyHWoGv5IHohnF+0y9xw1Hc0=; b=oYJOXj4hukhixP9Lp/YhX+mrGoOHmENKZCqb5QXf59taNEzoNQn4gNUnioiQnzAEap TcggBrhAkzaXrtSTxORkZUQzkdbrNe56JJ3eNfUnwEYtex/25bhVgWYNGfXrb2R3wdQQ lffdB8IQcpQ9rSRvbaAyp5aaobUey7vMJD6gO5gyACTZs5S1Tm8X6HG1xJ9m2UCcd9lb CZTOVn+N5NDQWxiqwPRKnfPTsmZikOE68OO6wq61gOL7moVBG+YPuhXpaQRZMUPFzrjt stvVct+vEbFTfkgN/WkeLklNqzJC/bokB+1fWDw78BKH6qw9a+FbAqeeRhiXUQYFJFhD kmNQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version; bh=TyYwTxr/bbnMT2s7IdFCyHWoGv5IHohnF+0y9xw1Hc0=; b=NKehCHUsOo18XLQ1Ja1tzrYPhS+lIlS2bNvEOjgOsn5ftoHuWXLRHjrDgpJqc643VC vyy+cfQwXtHtPjo6xpRykR7ugqVJiGfN26h2U0JPABlBh76kxlXCwNNU2GHlCDfFdyHQ SKH41BanOhWUxwHsyvg/SlpvZG605TYRbfA1Dh1oNWS+hINwQNlSNMWm1qzDdmTwgm2O iK9QfbcylERzlwWjVL6fXgyKtaAe6hH9ievwiatu6Au4edRbjRz1zdy/2JguyX2v2Q7s NyitmRxwK9pFmT/GFeIbpYhxucgOvB4EF4yRIMnONZZcMKWJ3EuHa25XuGMC1kFVUUja 6i8w== X-Gm-Message-State: AOAM5331j+6tsycWKJMtsXdTP8XTyczyQ/D+q3CmliywMkDFqnpeWx1o TkN7wBoV2DXlJ70DZgt7opABpA== X-Google-Smtp-Source: ABdhPJzOGDZpxf1G0r4cHJ2IbaH+Q/Dk5K73HNI5Jsp+DgiUBa1UsMa84YXwrZkQhLFfVPuTRFBurA== X-Received: by 2002:a9d:650f:: with SMTP id i15mr1013648otl.347.1609881232257; Tue, 05 Jan 2021 13:13:52 -0800 (PST) Received: from eggly.attlocal.net (172-10-233-147.lightspeed.sntcca.sbcglobal.net. [172.10.233.147]) by smtp.gmail.com with ESMTPSA id i16sm87516otc.61.2021.01.05.13.13.51 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Tue, 05 Jan 2021 13:13:51 -0800 (PST) Date: Tue, 5 Jan 2021 13:13:40 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Linus Torvalds cc: Hugh Dickins , Andrew Morton , Matthew Wilcox , syzbot , Linux Kernel Mailing List , Linux-MM , syzkaller-bugs Subject: Re: kernel BUG at mm/page-writeback.c:LINE! In-Reply-To: Message-ID: References: <000000000000886dbd05b7ffa8db@google.com> <20210104124153.0992b1f7fd1a145e193a333f@linux-foundation.org> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 5 Jan 2021, Linus Torvalds wrote: > On Tue, Jan 5, 2021 at 11:31 AM Linus Torvalds > wrote: > > On Mon, Jan 4, 2021 at 7:29 PM Hugh Dickins wrote: > > > > > > > So the one-liner of changing the "if" to "while" in > > > > wait_on_page_writeback() should get us back to what we used to do. > > > > > > I think that is the realistic way to go. > > > > Yeah, that's what I'll do. > > I took your "way to go" statement as an ack, and made it all be commit > c2407cf7d22d ("mm: make wait_on_page_writeback() wait for multiple > pending writebacks"). Great, thanks, I see it now. 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. But if it were reverted, we'd need some other fix for the PageTail part of it; and I still cannot think of anywhere else where we knowingly operated on a struct page without holding a reference; and there have been no adverse reports on its extra get_page+put_page. So I think it's safest to leave it in. Hugh