Re: [PATCH v2] mm: page_alloc: ignore init_on_free=1 for debug_pagealloc=1

[Vlastimil Babka]

On 3/27/21 7:21 PM, Sergei Trofimovich wrote:
> On !ARCH_SUPPORTS_DEBUG_PAGEALLOC (like ia64) debug_pagealloc=1
> implies page_poison=on:
> 
>     if (page_poisoning_enabled() ||
>          (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
>           debug_pagealloc_enabled()))
>             static_branch_enable(&_page_poisoning_enabled);
> 
> page_poison=on needs to init_on_free=1.
> 
> Before the change id happened too late for the following case:
> - have PAGE_POISONING=y
> - have page_poison unset
> - have !ARCH_SUPPORTS_DEBUG_PAGEALLOC arch (like ia64)
> - have init_on_free=1
> - have debug_pagealloc=1
> 
> That way we get both keys enabled:
> - static_branch_enable(&init_on_free);
> - static_branch_enable(&_page_poisoning_enabled);
> 
> which leads to poisoned pages returned for __GFP_ZERO pages.

Good catch, thanks for finding the root cause!

> After the change we execute only:
> - static_branch_enable(&_page_poisoning_enabled);
> and ignore init_on_free=1.
> CC: Vlastimil Babka <vbabka@xxxxxxx>
> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> CC: linux-mm@xxxxxxxxx
> CC: David Hildenbrand <david@xxxxxxxxxx>
> CC: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Link: https://lkml.org/lkml/2021/3/26/443
> Signed-off-by: Sergei Trofimovich <slyfox@xxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
8db26a3d4735 ("mm, page_poison: use static key more efficiently")
Cc: <stable@xxxxxxxxxxxxxxx>

> ---
>  mm/page_alloc.c | 30 +++++++++++++++++-------------
>  1 file changed, 17 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d57d9b4f7089..10a8a1d28c11 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -764,32 +764,36 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
>   */
>  void init_mem_debugging_and_hardening(void)
>  {
> +	bool page_poison_requested = page_poisoning_enabled();
> +
> +#ifdef CONFIG_PAGE_POISONING
> +	/*
> +	 * Page poisoning is debug page alloc for some arches. If
> +	 * either of those options are enabled, enable poisoning.
> +	 */
> +	if (page_poisoning_enabled() ||
> +	     (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
> +	      debug_pagealloc_enabled())) {
> +		static_branch_enable(&_page_poisoning_enabled);
> +		page_poison_requested = true;
> +	}
> +#endif
> +
>  	if (_init_on_alloc_enabled_early) {
> -		if (page_poisoning_enabled())
> +		if (page_poison_requested)
>  			pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
>  				"will take precedence over init_on_alloc\n");
>  		else
>  			static_branch_enable(&init_on_alloc);
>  	}
>  	if (_init_on_free_enabled_early) {
> -		if (page_poisoning_enabled())
> +		if (page_poison_requested)
>  			pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
>  				"will take precedence over init_on_free\n");
>  		else
>  			static_branch_enable(&init_on_free);
>  	}
>  
> -#ifdef CONFIG_PAGE_POISONING
> -	/*
> -	 * Page poisoning is debug page alloc for some arches. If
> -	 * either of those options are enabled, enable poisoning.
> -	 */
> -	if (page_poisoning_enabled() ||
> -	     (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
> -	      debug_pagealloc_enabled()))
> -		static_branch_enable(&_page_poisoning_enabled);
> -#endif
> -
>  #ifdef CONFIG_DEBUG_PAGEALLOC
>  	if (!debug_pagealloc_enabled())
>  		return;
>