linux-kernel - Re: [PATCH v2 4/4] mm: page_owner: use new iteration API

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Message-ID: <a196d780-c775-4f77-96f2-df3fe61af32f@redhat.com>
Date: Tue, 25 Feb 2025 17:44:58 +0100
From: David Hildenbrand <david@...hat.com>
To: Luiz Capitulino <luizcap@...hat.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, yuzhao@...gle.com, pasha.tatashin@...een.com
Cc: akpm@...ux-foundation.org, hannes@...xchg.org, muchun.song@...ux.dev
Subject: Re: [PATCH v2 4/4] mm: page_owner: use new iteration API

On 24.02.25 22:59, Luiz Capitulino wrote:
> The page_ext_next() function assumes that page extension objects for a
> page order allocation always reside in the same memory section, which
> may not be true and could lead to crashes. Use the new page_ext
> iteration API instead.
> 
> Fixes: cf54f310d0d3 ("mm/hugetlb: use __GFP_COMP for gigantic folios")
> Signed-off-by: Luiz Capitulino <luizcap@...hat.com>
> ---
>   mm/page_owner.c | 61 +++++++++++++++++++++++--------------------------
>   1 file changed, 29 insertions(+), 32 deletions(-)
> 

[...]

>   void __reset_page_owner(struct page *page, unsigned short order)
> @@ -293,11 +297,11 @@ void __reset_page_owner(struct page *page, unsigned short order)
>   
>   	page_owner = get_page_owner(page_ext);
>   	alloc_handle = page_owner->handle;
> +	page_ext_put(page_ext);
>   
>   	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
> -	__update_page_owner_free_handle(page_ext, handle, order, current->pid,
> +	__update_page_owner_free_handle(page, handle, order, current->pid,
>   					current->tgid, free_ts_nsec);
> -	page_ext_put(page_ext);

I assume moving that is fine ...

but I'll not that ...

> -	for (i = 0; i < (1 << new_page_owner->order); i++) {
> +	rcu_read_lock();
> +	for_each_page_ext(&old->page, 1 << new_page_owner->order, page_ext, iter) {
> +		old_page_owner = get_page_owner(page_ext);
>   		old_page_owner->handle = migrate_handle;
> -		old_ext = page_ext_next(old_ext);
> -		old_page_owner = get_page_owner(old_ext);
>   	}
> +	rcu_read_unlock();
>   
>   	page_ext_put(new_ext);
>   	page_ext_put(old_ext);

... here you are not moving it?


In general, LGTM, only the remaining page_ext_put() are a bit confusing.

-- 
Cheers,

David / dhildenb