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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 03900C43441 for ; Fri, 9 Nov 2018 10:08:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CB42920840 for ; Fri, 9 Nov 2018 10:08:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CB42920840 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=i-love.sakura.ne.jp 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 S1728396AbeKITsS (ORCPT ); Fri, 9 Nov 2018 14:48:18 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:53028 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727653AbeKITsR (ORCPT ); Fri, 9 Nov 2018 14:48:17 -0500 Received: from fsav104.sakura.ne.jp (fsav104.sakura.ne.jp [27.133.134.231]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id wA9A7nKj024467; Fri, 9 Nov 2018 19:07:49 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav104.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav104.sakura.ne.jp); Fri, 09 Nov 2018 19:07:49 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav104.sakura.ne.jp) Received: from [192.168.1.8] (softbank060157065137.bbtec.net [60.157.65.137]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id wA9A7mv9024433 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NO); Fri, 9 Nov 2018 19:07:48 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: UBSAN: Undefined behaviour in mm/page_alloc.c To: Michal Hocko 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 References: <20181109084353.GA5321@dhcp22.suse.cz> <20181109095604.GC5321@dhcp22.suse.cz> From: Tetsuo Handa Message-ID: Date: Fri, 9 Nov 2018 19:07:49 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 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 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.