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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 C2E79C43441 for ; Fri, 9 Nov 2018 10:10:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8295720840 for ; Fri, 9 Nov 2018 10:10:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8295720840 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz 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 S1728478AbeKITt4 (ORCPT ); Fri, 9 Nov 2018 14:49:56 -0500 Received: from mx2.suse.de ([195.135.220.15]:48504 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727663AbeKITt4 (ORCPT ); Fri, 9 Nov 2018 14:49:56 -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 0BCFFABDC; Fri, 9 Nov 2018 10:10:01 +0000 (UTC) Subject: Re: UBSAN: Undefined behaviour in mm/page_alloc.c To: Michal Hocko , Tetsuo Handa Cc: 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 References: <20181109084353.GA5321@dhcp22.suse.cz> <20181109095604.GC5321@dhcp22.suse.cz> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181109095604.GC5321@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/9/18 10:56 AM, Michal Hocko wrote: > On Fri 09-11-18 18:41:53, Tetsuo Handa wrote: >> On 2018/11/09 17:43, Michal Hocko wrote: >>> @@ -4364,6 +4353,17 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int preferred_nid, >>> gfp_t alloc_mask; /* The gfp_t that was actually used for allocation */ >>> struct alloc_context ac = { }; >>> >>> + /* >>> + * In the slowpath, we sanity check order to avoid ever trying to >> >> Please keep the comment up to dated. > > Does this following look better? > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 9fc10a1029cf..bf9aecba4222 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4354,10 +4354,8 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int preferred_nid, > struct alloc_context ac = { }; > > /* > - * In the slowpath, we sanity check order to avoid ever trying to > - * reclaim >= MAX_ORDER areas which will never succeed. Callers may > - * be using allocators in order of preference for an area that is > - * too large. > + * There are several places where we assume that the order value is sane > + * so bail out early if the request is out of bound. > */ > if (order >= MAX_ORDER) { > WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN)); Looks ok, but I'd add unlikely(), although it doesn't currently seem to make any difference. You can add Acked-by: Vlastimil Babka >> I don't like that comments in OOM code is outdated. >> >>> + * 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.