linux-kernel - Re: [PATCH 1/3] mm, page_alloc: do not rely on the order of page_poison and init_on

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Date:   Wed, 28 Oct 2020 10:31:12 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Alexander Potapenko <glider@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Michal Hocko <mhocko@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Mateusz Nosek <mateusznosek0@...il.com>
Subject: Re: [PATCH 1/3] mm, page_alloc: do not rely on the order of
 page_poison and init_on_alloc/free parameters

On Mon, Oct 26, 2020 at 06:33:56PM +0100, Vlastimil Babka wrote:
> Enabling page_poison=1 together with init_on_alloc=1 or init_on_free=1 produces
> a warning in dmesg that page_poison takes precendence. However, as these

                                          ^ precedence

> warnings are printed in early_param handlers for init_on_alloc/free, they are
> not printed if page_poison is enabled later on the command line (handlers are
> called in the order of their parameters), or when init_on_alloc/free is always
> enabled by the respective config option - before the page_poison early param
> handler is called, it is not considered to be enabled. This is inconsistent.
> 
> We can remove the dependency on order by making the init_on_* parameters only
> set a boolean variable, and postponing the evaluation after all early params
> have been processed. Introduce a new init_mem_debugging() function for that,
> and move the related debug_pagealloc processing there as well.
> 
> As a result init_mem_debugging() knows always accurately if init_on_* and/or
> page_poison options were enabled. Thus we can also optimize want_init_on_alloc()
> and want_init_on_free(). We don't need to check page_poisoning_enabled() there,
> we can instead not enable the init_on_* tracepoint at all, if page poisoning is
> enabled. This results in a simpler and more effective code.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

With two more nits below fixed

Reviewed-by: Mike Rapoport <rppt@...ux.ibm.com>

> ---
>  include/linux/mm.h | 20 ++--------
>  init/main.c        |  2 +-
>  mm/page_alloc.c    | 94 +++++++++++++++++++++++-----------------------
>  3 files changed, 50 insertions(+), 66 deletions(-)
> 

...

> @@ -792,6 +752,44 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
>  				unsigned int order, int migratetype) {}
>  #endif
>  
> +/*
> + * Enable static keys related to various memory debugging and hardening options.
> + * Some override others, and depend on early params that are evaluated in the
> + * order of appearance. So we need to first gather the full picture of what was
> + * enabled, and then make decisions.
> + */
> +void init_mem_debugging()

Shouldn't it be init_mem_debug(void)?
Or whatever a new name would be :)

> +{
> +	if (_init_on_alloc_enabled_early) {
> +		if (page_poisoning_enabled()) {
> +			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()) {
> +			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);
> +		}
> +	}

I think the braces for the inner ifs are not required.

> +
> +#ifdef CONFIG_DEBUG_PAGEALLOC
> +	if (!debug_pagealloc_enabled())
> +		return;
> +
> +	static_branch_enable(&_debug_pagealloc_enabled);
> +
> +	if (!debug_guardpage_minorder())
> +		return;
> +
> +	static_branch_enable(&_debug_guardpage_enabled);
> +#endif
> +}
> +
>  static inline void set_buddy_order(struct page *page, unsigned int order)
>  {
>  	set_page_private(page, order);
> -- 
> 2.29.0
> 
> 

-- 
Sincerely yours,
Mike.