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=-5.5 required=3.0 tests=INCLUDES_PATCH, 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 DA119C43441 for ; Fri, 9 Nov 2018 09:56:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A6E7520883 for ; Fri, 9 Nov 2018 09:56:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A6E7520883 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 S1727999AbeKITf6 (ORCPT ); Fri, 9 Nov 2018 14:35:58 -0500 Received: from mx2.suse.de ([195.135.220.15]:39800 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727537AbeKITf5 (ORCPT ); Fri, 9 Nov 2018 14:35:57 -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 AE4D6ADDD; Fri, 9 Nov 2018 09:56:06 +0000 (UTC) Date: Fri, 9 Nov 2018 10:56:04 +0100 From: Michal Hocko To: Tetsuo Handa Cc: Kyungtae Kim , akpm@linux-foundation.org, pavel.tatashin@microsoft.com, vbabka@suse.cz, 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: <20181109095604.GC5321@dhcp22.suse.cz> References: <20181109084353.GA5321@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 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)); > 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? -- Michal Hocko SUSE Labs