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 C3542C43441 for ; Fri, 9 Nov 2018 10:29:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 939C120827 for ; Fri, 9 Nov 2018 10:29:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 939C120827 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 S1727828AbeKIUJA (ORCPT ); Fri, 9 Nov 2018 15:09:00 -0500 Received: from mx2.suse.de ([195.135.220.15]:56084 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727537AbeKIUJA (ORCPT ); Fri, 9 Nov 2018 15:09:00 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id C86ACAE11; Fri, 9 Nov 2018 10:29:00 +0000 (UTC) Date: Fri, 9 Nov 2018 11:28:55 +0100 From: Michal Hocko To: Tetsuo Handa Cc: Vlastimil Babka , Kyungtae Kim , akpm@linux-foundation.org, pavel.tatashin@microsoft.com, osalvador@suse.de, rppt@linux.vnet.ibm.com, aaron.lu@intel.com, iamjoonsoo.kim@lge.com, alexander.h.duyck@linux.intel.com, mgorman@techsingularity.net, lifeasageek@gmail.com, threeearcat@gmail.com, syzkaller@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Konstantin Khlebnikov Subject: Re: UBSAN: Undefined behaviour in mm/page_alloc.c Message-ID: <20181109102855.GF5321@dhcp22.suse.cz> References: <20181109084353.GA5321@dhcp22.suse.cz> <20181109095604.GC5321@dhcp22.suse.cz> <9e17d033-b2ab-3edb-ae0b-90d4f713e55b@i-love.sakura.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9e17d033-b2ab-3edb-ae0b-90d4f713e55b@i-love.sakura.ne.jp> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 09-11-18 19:24:48, Tetsuo Handa wrote: > On 2018/11/09 19:10, Vlastimil Babka wrote:>>>> + * reclaim >= MAX_ORDER areas which will never succeed. Callers may > >>>> + * be using allocators in order of preference for an area that is > >>>> + * too large. > >>>> + */ > >>>> + if (order >= MAX_ORDER) { > >>> > >>> Also, why not to add BUG_ON(gfp_mask & __GFP_NOFAIL); here? > >> > >> Because we do not want to blow up the kernel just because of a stupid > >> usage of the allocator. Can you think of an example where it would > >> actually make any sense? > >> > >> I would argue that such a theoretical abuse would blow up on an > >> unchecked NULL ptr access. Isn't that enough? > > > > Agreed. > > > > If someone has written a module with __GFP_NOFAIL for an architecture > where PAGE_SIZE == 2048KB, and someone else tried to use that module on > another architecture where PAGE_SIZE == 4KB. You are saying that > triggering NULL pointer dereference is a fault of that user's ignorance > about MM. You are saying that everyone knows internal of MM. Sad... What kind of argument is this? Seriously! We do consider GFP_NOFAIL problematic even for !order-0 requests and warn appropriately. Talking about anything getting close to MAX_ORDER is just a crazy talk. In any case this is largely tangential to the issue reported here. -- Michal Hocko SUSE Labs