linux-kernel - Re: [PATCH v1 1/8] kasan: Change the behavior of kmalloc_large_oob

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Date:	Mon, 1 Feb 2016 21:34:27 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alexander Potapenko <glider@...gle.com>
Cc:	adech.fo@...il.com, cl@...ux.com, dvyukov@...gle.com,
	ryabinin.a.a@...il.com, rostedt@...dmis.org,
	kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH v1 1/8] kasan: Change the behavior of
 kmalloc_large_oob_right test

On Wed, 27 Jan 2016 19:25:06 +0100 Alexander Potapenko <glider@...gle.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.