linux-kernel - Re: [RFC V2] mm: add the zero case to page[1].compound_nr in set_compound

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Date:   Tue, 13 Dec 2022 15:47:54 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Nico Pache <npache@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        muchun.song@...ux.dev, akpm@...ux-foundation.org,
        willy@...radead.org, gerald.schaefer@...ux.ibm.com
Subject: Re: [RFC V2] mm: add the zero case to page[1].compound_nr in
 set_compound_order

On 12/13/22 16:45, Nico Pache wrote:
> Since commit 1378a5ee451a ("mm: store compound_nr as well as
> compound_order") the page[1].compound_nr must be explicitly set to 0 if
> calling set_compound_order(page, 0).
> 
> This can lead to bugs if the caller of set_compound_order(page, 0) forgets
> to explicitly set compound_nr=0. An example of this is commit ba9c1201beaa
> ("mm/hugetlb: clear compound_nr before freeing gigantic pages")

There has been some recent work in this area.  The latest patch being,          
https://lore.kernel.org/linux-mm/20221213212053.106058-1-sidhartha.kumar@oracle.com/

-- 
Mike Kravetz