From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 717D36B06D2 for ; Fri, 9 Nov 2018 05:22:39 -0500 (EST) Received: by mail-ed1-f70.google.com with SMTP id m45-v6so950593edc.2 for ; Fri, 09 Nov 2018 02:22:39 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id jr1-v6si525783ejb.232.2018.11.09.02.22.37 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 09 Nov 2018 02:22:38 -0800 (PST) Date: Fri, 9 Nov 2018 11:22:35 +0100 From: Michal Hocko Subject: Re: UBSAN: Undefined behaviour in mm/page_alloc.c Message-ID: <20181109102235.GD5321@dhcp22.suse.cz> References: <20181109084353.GA5321@dhcp22.suse.cz> <20181109095604.GC5321@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: Tetsuo Handa , 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 On Fri 09-11-18 11:10:00, Vlastimil Babka wrote: > 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 OK, I have added both. Thanks! -- Michal Hocko SUSE Labs