From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S933286AbcBBP2c (ORCPT <rfc822;w@1wt.eu>);
	Tue, 2 Feb 2016 10:28:32 -0500
Received: from mail-lb0-f173.google.com ([209.85.217.173]:36090 "EHLO
	mail-lb0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S933125AbcBBP22 (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 2 Feb 2016 10:28:28 -0500
Subject: Re: [PATCH v1 1/8] kasan: Change the behavior of
 kmalloc_large_oob_right test
To: Andrew Morton <akpm@linux-foundation.org>,
        Alexander Potapenko <glider@google.com>
References: <cover.1453918525.git.glider@google.com>
 <35b553cafcd5b77838aeaf5548b457dfa09e30cf.1453918525.git.glider@google.com>
 <20160201213427.f428b08d.akpm@linux-foundation.org>
Cc: adech.fo@gmail.com, cl@linux.com, dvyukov@google.com, rostedt@goodmis.org,
        kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
From: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Message-ID: <56B0CB60.1080506@gmail.com>
Date: Tue, 2 Feb 2016 18:29:36 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.5.0
MIME-Version: 1.0
In-Reply-To: <20160201213427.f428b08d.akpm@linux-foundation.org>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org



On 02/02/2016 08:34 AM, Andrew Morton wrote:
> On Wed, 27 Jan 2016 19:25:06 +0100 Alexander Potapenko <glider@google.com> wrote:
> 
>> depending on which allocator (SLAB or SLUB) is being used
>>
>> ...
>>
>> --- a/lib/test_kasan.c
>> +++ b/lib/test_kasan.c
>> @@ -68,7 +68,22 @@ static noinline void __init kmalloc_node_oob_right(void)
>>  static noinline void __init kmalloc_large_oob_right(void)
>>  {
>>  	char *ptr;
>> -	size_t size = KMALLOC_MAX_CACHE_SIZE + 10;
>> +	size_t size;
>> +
>> +	if (KMALLOC_MAX_CACHE_SIZE == KMALLOC_MAX_SIZE) {
>> +		/*
>> +		 * We're using the SLAB allocator. Allocate a chunk that fits
>> +		 * into a slab.
>> +		 */
>> +		size = KMALLOC_MAX_CACHE_SIZE - 256;
>> +	} else {
>> +		/*
>> +		 * KMALLOC_MAX_SIZE > KMALLOC_MAX_CACHE_SIZE.
>> +		 * We're using the SLUB allocator. Allocate a chunk that does
>> +		 * not fit into a slab to trigger the page allocator.
>> +		 */
>> +		size = KMALLOC_MAX_CACHE_SIZE + 10;
>> +	}
> 
> This seems a weird way of working out whether we're using SLAB or SLUB.
> 
> Can't we use, umm, #ifdef CONFIG_SLAB?  If not that then let's cook up
> something standardized rather than a weird just-happens-to-work like
> this.
> 

Actually it would be simpler to not use KMALLOC_MAX_CACHE_SIZE at all.
Simply replace it with 2 or 3 PAGE_SIZEs.