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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 A6083C43144 for ; Wed, 27 Jun 2018 07:39:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 46C2F23FE1 for ; Wed, 27 Jun 2018 07:39:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 46C2F23FE1 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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 S1753413AbeF0Hjj (ORCPT ); Wed, 27 Jun 2018 03:39:39 -0400 Received: from mx2.suse.de ([195.135.220.15]:40625 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751239AbeF0Hji (ORCPT ); Wed, 27 Jun 2018 03:39:38 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (charybdis-ext-too.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 49A18ABDD; Wed, 27 Jun 2018 07:39:37 +0000 (UTC) Date: Wed, 27 Jun 2018 09:39:36 +0200 From: Michal Hocko To: Andrew Morton Cc: Vlastimil Babka , JianKang Chen , Mel Gorman , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org, xieyisheng1@huawei.com, guohanjun@huawei.com, wangkefeng.wang@huawei.com Subject: Re: [PATCH] mm: drop VM_BUG_ON from __get_free_pages Message-ID: <20180627073936.GE32348@dhcp22.suse.cz> References: <20180622162841.25114-1-mhocko@kernel.org> <6886dee0-3ac4-ef5d-3597-073196c81d88@suse.cz> <20180626100416.a3ff53f5c4aac9fae954e3f6@linux-foundation.org> <20180627073420.GD32348@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180627073420.GD32348@dhcp22.suse.cz> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 27-06-18 09:34:20, Michal Hocko wrote: > On Tue 26-06-18 10:04:16, Andrew Morton wrote: [...] > > Really, the changelog isn't right. There *is* a real reason to blow > > up. Effectively the caller is attempting to obtain the virtual address > > of a highmem page without having kmapped it first. That's an outright > > bug. > > And as I've argued before the code would be wrong regardless. We would > leak the memory or worse touch somebody's else kmap without knowing > that. So we have a choice between a mem leak, data corruption k or a > silent fixup. I would prefer the last option. And blowing up on a BUG > is not much better on something that is easily fixable. I am not really > convinced that & ~__GFP_HIGHMEM is something to lose sleep over. It's been some time since I've checked that changelog and you are right it should contain all the above so the changelog should be: " There is no real reason to blow up just because the caller doesn't know that __get_free_pages cannot return highmem pages. Simply fix that up silently. Even if we have some confused users such a fixup will not be harmful. On the other hand an incorrect usage can lead to either a memory leak or worse a memory corruption when the allocated page hashes to an already kmaped page. Most workloads run with CONFIG_DEBUG_VM disabled so the assert wouldn't help. " -- Michal Hocko SUSE Labs