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 38DA7C43441 for ; Fri, 9 Nov 2018 10:25:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 08E8E20827 for ; Fri, 9 Nov 2018 10:25:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 08E8E20827 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 S1728006AbeKIUFf (ORCPT ); Fri, 9 Nov 2018 15:05:35 -0500 Received: from mx2.suse.de ([195.135.220.15]:55672 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727537AbeKIUFf (ORCPT ); Fri, 9 Nov 2018 15:05:35 -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 CBB08AE11; Fri, 9 Nov 2018 10:25:36 +0000 (UTC) Date: Fri, 9 Nov 2018 11:25:36 +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: <20181109102536.GE5321@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: 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 19:07:49, Tetsuo Handa wrote: > On 2018/11/09 18:56, Michal Hocko wrote: > > Does this following look better? > > Yes. > > >> 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? > > We after all can't avoid blowing up the kernel even if we don't add BUG_ON(). > Stopping with BUG_ON() is saner than NULL pointer dereference messages. I disagree (strongly to be more explicit). You never know the context the allocator is called from. We do not want to oops with a random state (locks heled etc). If the access blows up in the user then be it, the bug will be clear and to be fixed but BUG_ON on an invalid core kernel function is just a bad idea. I believe Linus was quite explicit about it and I fully agree with him. Besides that this is really off-topic to the issue at hands. Don't you think? -- Michal Hocko SUSE Labs