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=-3.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIMWL_WL_MED, USER_AGENT_NEOMUTT autolearn=ham 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 074D6C43142 for ; Tue, 31 Jul 2018 06:29:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9F85D208A4 for ; Tue, 31 Jul 2018 06:29:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=shutemov-name.20150623.gappssmtp.com header.i=@shutemov-name.20150623.gappssmtp.com header.b="m8fkrXB6" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9F85D208A4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=shutemov.name Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729762AbeGaIIQ (ORCPT ); Tue, 31 Jul 2018 04:08:16 -0400 Received: from mail-pl0-f68.google.com ([209.85.160.68]:34376 "EHLO mail-pl0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727409AbeGaIIP (ORCPT ); Tue, 31 Jul 2018 04:08:15 -0400 Received: by mail-pl0-f68.google.com with SMTP id f6-v6so6707248plo.1 for ; Mon, 30 Jul 2018 23:29:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shutemov-name.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=4op/UZBvIySF+WDKzYy4Yd56uknU6JHQLEzUDmr7W94=; b=m8fkrXB6wK/X0UMFDFyndbm9Z/ar0bRMzefDY6fTz60e1Ez2lbFo3v1aoVdfXTrq/S dwtvg77BITfEIPsIU9lzNbP0fzXYk0/Cj6kWW3aGkgW7gQrVZlhgmUJNJza6xhqdNwqI PLnr9/h2OWcVoukEZFWYRTVN1uiUU3HdAB2tHvpfXNir9/+tJcmgzgOmR8Os3WsbINIT 9L+ECm3wTNToX6UozSclQEDAZXf8uVGepcCkfxYdoJhgtHy17Yv85wn0aSLLC4Npo1jV dkdyqQoqkJNt51Fxm9O/PDQHaijYY1haDUcWyuFRVsU4SKVD9D6IUMhTKyFEQUh4wCXt VP5g== 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:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=4op/UZBvIySF+WDKzYy4Yd56uknU6JHQLEzUDmr7W94=; b=r8s+pO2gOw/XgDXKLm7vvBTRYAiP98bingJwC9fCDNR9S6EYYW5tlvhbIpNaQ2At53 l99+1YG1bEE6zXHksDG4IzFlKn4+iz9QOwqTuuRyB8PcGqbQd2ITtLYCtLDFBcaN23zl DQQ2ky4g76YaK+Fs3UOLKd0qnJ+7QU/LfnAKl5hXHo7Nxb2bGVp7Ec26rJ3su8pSLVBD lpIzqKCuAHUJTfnaDzxC/XshAuI8ipUodLB1piSHkumRxn/rpt/0nqLhnyALbo3MGbbP QyYUkCFwE+o/9XTIQ7XBp9BsCDOVF1cwPePW9KO/J1EI+VDL/LpozUjkig0WgYLj1/UJ rC6w== X-Gm-Message-State: AOUpUlHJIjTscXposoKXt5vXFIR/0wMbKdjoCaSF60+1V3INaQtK8IiR MfaY0WI8uRS+aeNg32SOVCv+Ug== X-Google-Smtp-Source: AAOMgpcmUy4qeW7M8OZ94th6u+dps5pWNHsOHonZQU9HZ3n4hWF7hL0kbcn7e6CAqpVXfQZW6bQDvg== X-Received: by 2002:a17:902:aa87:: with SMTP id d7-v6mr19208489plr.215.1533018573292; Mon, 30 Jul 2018 23:29:33 -0700 (PDT) Received: from kshutemo-mobl1.localdomain ([134.134.139.83]) by smtp.gmail.com with ESMTPSA id m4-v6sm18577694pgn.82.2018.07.30.23.29.32 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 30 Jul 2018 23:29:32 -0700 (PDT) Received: by kshutemo-mobl1.localdomain (Postfix, from userid 1000) id A8FD43002A5; Tue, 31 Jul 2018 09:29:27 +0300 (+03) Date: Tue, 31 Jul 2018 09:29:27 +0300 From: "Kirill A. Shutemov" To: Linus Torvalds Cc: Hugh Dickins , Matthew Wilcox , Amit Pundir , "Kirill A. Shutemov" , Andrew Morton , Dmitry Vyukov , Oleg Nesterov , Andrea Arcangeli , Greg Kroah-Hartman , John Stultz , linux-mm , Linux Kernel Mailing List , youling257@gmail.com Subject: Re: Linux 4.18-rc7 Message-ID: <20180731062927.hjknfcb2cj3bwd7b@kshutemo-mobl1> References: <20180730130134.yvn5tcmoavuxtwt5@kshutemo-mobl1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 30, 2018 at 06:01:26PM -0700, Linus Torvalds wrote: > On Mon, Jul 30, 2018 at 2:53 PM Hugh Dickins wrote: > > > > I have no problem with reverting -rc7's vma_is_anonymous() series. > > I don't think we need to revert the whole series: I think the rest are > all fairly obvious cleanups, and shouldn't really have any semantic > changes. > > It's literally only that last patch in the series that then changes > that meaning of "vm_ops". And I don't really _mind_ that last step > either, but since we don't know exactly what it was that it broke, and > we're past rc7, I don't think we really have any option but the revert > it. > > And if we revert it, I think we need to just remove the > VM_BUG_ON_VMA() that it was supposed to fix. Because I do think that > it is quite likely that the real bug is that overzealous BUG_ON(), > since I can't see any reason why anonymous mappings should be special > there. > > But I'm certainly also ok with re-visiting that commit later. I just > think that right _now_ the above is my preferred plan. > > Kirill? Considering the timing, I'm okay with reverting the last patch with dropping the VM_BUG_ON_VMA(). But in the end I would like to see strong vma_is_anonymous(). The VM_BUG_ON_VMA() is only triggerable by the test case because vma_is_anonymous() false-positive in fault path and we get anon-THP allocated in file-private mapping. I don't see immediately how this may trigger other crashes. But it definitely looks wrong. > > I'm all for deleting that VM_BUG_ON_VMA() in zap_pmd_range(), it was > > just a compromise with those who wanted to keep something there; > > I don't think we even need a WARN_ON_ONCE() now. > > So to me it looks like a historical check that simply doesn't > "normally" trigger, but there's no reason I can see why we should care > about the case it tests against. I'll think more on what could go wrong with __split_huge_pmd() called on anon-THP page without mmap_sem(). It's not yet clear cut to me. -- Kirill A. Shutemov