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

From: Qian Cai <[email-masked]>
Date: Thu, 12 Sep 2019 10:10:15 -0400

On Thu, 2019-09-12 at 15:53 +0200, Vlastimil Babka wrote:
> On 9/11/19 5:19 PM, Qian Cai wrote:
> > 
> > The new config looks redundant and confusing. It looks to me more of a document update
> > in Documentation/dev-tools/kasan.txt to educate developers to select PAGE_OWNER and
> > DEBUG_PAGEALLOC if needed.
> 
>  
> Agreed. But if you want it fully automatic, how about something
> like this (on top of mmotm/next)? If you agree I'll add changelog
> and send properly.
> 
> ----8<----
> 
> From a528d14c71d7fdf5872ca8ab3bd1b5bad26670c9 Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <[email-masked]>
> Date: Thu, 12 Sep 2019 15:51:23 +0200
> Subject: [PATCH] make KASAN enable page_owner with free stack capture
> 
> ---
>  include/linux/page_owner.h |  1 +
>  lib/Kconfig.kasan          |  4 ++++
>  mm/Kconfig.debug           |  5 +++++
>  mm/page_alloc.c            |  6 +++++-
>  mm/page_owner.c            | 37 ++++++++++++++++++++++++-------------
>  5 files changed, 39 insertions(+), 14 deletions(-)
> 
> diff --git a/include/linux/page_owner.h b/include/linux/page_owner.h
> index 8679ccd722e8..6ffe8b81ba85 100644
> --- a/include/linux/page_owner.h
> +++ b/include/linux/page_owner.h
> @@ -6,6 +6,7 @@
>  
>  #ifdef CONFIG_PAGE_OWNER
>  extern struct static_key_false page_owner_inited;
> +extern bool page_owner_free_stack_disabled;
>  extern struct page_ext_operations page_owner_ops;
>  
>  extern void __reset_page_owner(struct page *page, unsigned int order);
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index 6c9682ce0254..dc560c7562e8 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -41,6 +41,8 @@ config KASAN_GENERIC
>  	select SLUB_DEBUG if SLUB
>  	select CONSTRUCTORS
>  	select STACKDEPOT
> +	select PAGE_OWNER
> +	select PAGE_OWNER_FREE_STACK
>  	help
>  	  Enables generic KASAN mode.
>  	  Supported in both GCC and Clang. With GCC it requires version 4.9.2
> @@ -63,6 +65,8 @@ config KASAN_SW_TAGS
>  	select SLUB_DEBUG if SLUB
>  	select CONSTRUCTORS
>  	select STACKDEPOT
> +	select PAGE_OWNER
> +	select PAGE_OWNER_FREE_STACK
>  	help
>  	  Enables software tag-based KASAN mode.
>  	  This mode requires Top Byte Ignore support by the CPU and therefore

I don't know how KASAN people will feel about this. Especially, KASAN_SW_TAGS
was designed for people who complain about memory footprint of KASAN_GENERIC is
too high as far as I can tell.

I guess it depends on them to test the new memory footprint of KASAN to see if
they are happy with it.

> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> index 327b3ebf23bf..a71d52636687 100644
> --- a/mm/Kconfig.debug
> +++ b/mm/Kconfig.debug
> @@ -13,6 +13,7 @@ config DEBUG_PAGEALLOC
>  	depends on DEBUG_KERNEL
>  	depends on !HIBERNATION || ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC
>  	select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC
> +	select PAGE_OWNER_FREE_STACK if PAGE_OWNER
>  	---help---
>  	  Unmap pages from the kernel linear mapping after free_pages().
>  	  Depending on runtime enablement, this results in a small or large
> @@ -62,6 +63,10 @@ config PAGE_OWNER
>  
>  	  If unsure, say N.
>  
> +config PAGE_OWNER_FREE_STACK
> +	def_bool n
> +	depends on PAGE_OWNER
> +
>  config PAGE_POISONING
>  	bool "Poison pages after freeing"
>  	select PAGE_POISONING_NO_SANITY if HIBERNATION
> 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;
> +#endif
> +	}
>  
>  	return 0;
>  }
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index dee931184788..d4551d7012d0 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 +48,11 @@ static int __init early_page_owner_param(char *buf)
>  	if (strcmp(buf, "on") == 0)
>  		page_owner_disabled = false;
>  
> +	if (IS_ENABLED(CONFIG_KASAN)) {
> +		page_owner_disabled = false;
> +		page_owner_free_stack_disabled = false;
> +	}
> +
>  	return 0;
>  }
>  early_param("page_owner", early_page_owner_param);
> @@ -91,6 +98,8 @@ static void init_page_owner(void)
>  	register_failure_stack();
>  	register_early_stack();
>  	static_branch_enable(&page_owner_inited);
> +	if (!page_owner_free_stack_disabled)
> +		static_branch_enable(&page_owner_free_stack);
>  	init_early_allocated_pages();
>  }
>  
> @@ -148,11 +157,11 @@ void __reset_page_owner(struct page *page, unsigned int order)
>  {
>  	int i;
>  	struct page_ext *page_ext;
> -#ifdef CONFIG_DEBUG_PAGEALLOC
> +#ifdef CONFIG_PAGE_OWNER_FREE_STACK
>  	depot_stack_handle_t handle = 0;
>  	struct page_owner *page_owner;
>  
> -	if (debug_pagealloc_enabled())
> +	if (static_branch_unlikely(&page_owner_free_stack))
>  		handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
>  #endif
>  
> @@ -161,8 +170,8 @@ void __reset_page_owner(struct page *page, unsigned int order)
>  		if (unlikely(!page_ext))
>  			continue;
>  		__clear_bit(PAGE_EXT_OWNER_ACTIVE, &page_ext->flags);
> -#ifdef CONFIG_DEBUG_PAGEALLOC
> -		if (debug_pagealloc_enabled()) {
> +#ifdef CONFIG_PAGE_OWNER_FREE_STACK
> +		if (static_branch_unlikely(&page_owner_free_stack)) {
>  			page_owner = get_page_owner(page_ext);
>  			page_owner->free_handle = handle;
>  		}
> @@ -451,14 +460,16 @@ void __dump_page_owner(struct page *page)
>  		stack_trace_print(entries, nr_entries, 0);
>  	}
>  
> -#ifdef CONFIG_DEBUG_PAGEALLOC
> -	handle = READ_ONCE(page_owner->free_handle);
> -	if (!handle) {
> -		pr_alert("page_owner free stack trace missing\n");
> -	} else {
> -		nr_entries = stack_depot_fetch(handle, &entries);
> -		pr_alert("page last free stack trace:\n");
> -		stack_trace_print(entries, nr_entries, 0);
> +#ifdef CONFIG_PAGE_OWNER_FREE_STACK
> +	if (static_branch_unlikely(&page_owner_free_stack)) {
> +		handle = READ_ONCE(page_owner->free_handle);
> +		if (!handle) {
> +			pr_alert("page_owner free stack trace missing\n");
> +		} else {
> +			nr_entries = stack_depot_fetch(handle, &entries);
> +			pr_alert("page last free stack trace:\n");
> +			stack_trace_print(entries, nr_entries, 0);
> +		}
>  	}
>  #endif
>  

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