linux-kernel - Re: [PATCH v3] mm: page_alloc: ignore init_on_free=1 for debug

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Date:   Tue, 30 Mar 2021 10:39:40 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Sergei Trofimovich <slyfox@...too.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...il.com>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v3] mm: page_alloc: ignore init_on_free=1 for
 debug_pagealloc=1

On 30.03.21 00:25, 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 override init_on_free=1.
> 
> Before the change it did not work as expected 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.
> 
> After the change we execute only:
> - static_branch_enable(&_page_poisoning_enabled);
> and ignore init_on_free=1.
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> Fixes: 8db26a3d4735 ("mm, page_poison: use static key more efficiently")
> Cc: <stable@...r.kernel.org>
> CC: Andrew Morton <akpm@...ux-foundation.org>
> CC: linux-mm@...ck.org
> CC: David Hildenbrand <david@...hat.com>
> CC: Andrey Konovalov <andreyknvl@...il.com>
> Link: https://lkml.org/lkml/2021/3/26/443
> 
> Signed-off-by: Sergei Trofimovich <slyfox@...too.org>
> ---
> Change since v2:
> - Added 'Fixes:' and 'CC: stable@' suggested by Vlastimil and David
> - Renamed local variable to 'page_poisoning_requested' for
>    consistency suggested by David
> - Simplified initialization of page_poisoning_requested suggested
>    by David
> - Added 'Acked-by: Vlastimil'
> 
>   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 cfc72873961d..4bb3cdfc47f8 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_poisoning_requested = false;
> +
> +#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_poisoning_requested = true;
> +	}
> +#endif
> +
>   	if (_init_on_alloc_enabled_early) {
> -		if (page_poisoning_enabled())
> +		if (page_poisoning_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_poisoning_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;
> 

Thanks!

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb