Subject: Re: [PATCH v3] mm/kasan: dump alloc and free stack for page allocator

From: Andrey Ryabinin <[email-masked]>
Date: Mon, 16 Sep 2019 18:57:23 +0300

On 9/16/19 12:42 PM, Vlastimil Babka wrote:
> On 9/12/19 7:05 PM, Andrey Ryabinin wrote:
>>
>> Or another alternative option (and actually easier one to implement), leave PAGE_OWNER as is (no "select"s in Kconfigs)
>> Make PAGE_OWNER_FREE_STACK like this:
>>
>> +config PAGE_OWNER_FREE_STACK
>> +	def_bool KASAN || DEBUG_PAGEALLOC
>> +	depends on PAGE_OWNER
>> +
>>
>> So, users that want alloc/free stack will have to enable CONFIG_PAGE_OWNER=y and add page_owner=on to boot cmdline.
>>
>>
>> Basically the difference between these alternative is whether we enable page_owner by default or not. But there is always a possibility to disable it.
> 
> OK, how about this?
> 
 ...

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c5d62f1c2851..d9e44671af3f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -710,8 +710,12 @@ static int __init early_debug_pagealloc(char *buf)
>  	if (kstrtobool(buf, &enable))
>  		return -EINVAL;
>  
> -	if (enable)
> +	if (enable) {
>  		static_branch_enable(&_debug_pagealloc_enabled);
> +#ifdef CONFIG_PAGE_OWNER
> +		page_owner_free_stack_disabled = false;

I think this won't work with CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT=y

> +#endif
> +	}
>  
>  	return 0;
>  }
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index dee931184788..b589bfbc4795 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -24,13 +24,15 @@ struct page_owner {
>  	short last_migrate_reason;
>  	gfp_t gfp_mask;
>  	depot_stack_handle_t handle;
> -#ifdef CONFIG_DEBUG_PAGEALLOC
> +#ifdef CONFIG_PAGE_OWNER_FREE_STACK
>  	depot_stack_handle_t free_handle;
>  #endif
>  };
>  
>  static bool page_owner_disabled = true;
> +bool page_owner_free_stack_disabled = true;
>  DEFINE_STATIC_KEY_FALSE(page_owner_inited);
> +static DEFINE_STATIC_KEY_FALSE(page_owner_free_stack);
>  
>  static depot_stack_handle_t dummy_handle;
>  static depot_stack_handle_t failure_handle;
> @@ -46,6 +48,9 @@ static int __init early_page_owner_param(char *buf)
>  	if (strcmp(buf, "on") == 0)
>  		page_owner_disabled = false;
>  
> +	if (!page_owner_disabled && IS_ENABLED(CONFIG_KASAN))

I'd rather keep all logic in one place, i.e. "if (!page_owner_disabled && (IS_ENABLED(CONFIG_KASAN) || debug_pagealloc_enabled())"
With this no changes in early_debug_pagealloc() required and CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT=y should also work correctly.

> +		page_owner_free_stack_disabled = false;
> +
>  	return 0;
>  }
>  early_param("page_owner", early_page_owner_param);

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