linux-kernel - Re: [syzbot] [mm?] WARNING in follow_page

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Message-ID: <3d2c04e0-b164-41fb-922b-ad7c09075a62@redhat.com>
Date: Wed, 6 Aug 2025 14:21:51 +0200
From: David Hildenbrand <david@...hat.com>
To: Dev Jain <dev.jain@....com>,
 syzbot+57bcc752f0df8bb1365c@...kaller.appspotmail.com
Cc: akpm@...ux-foundation.org, jgg@...pe.ca, jhubbard@...dia.com,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, peterx@...hat.com,
 syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] WARNING in follow_page_pte

>   static void commit_anon_folio_batch(struct vm_area_struct *vma,
> -		struct folio *folio, unsigned long addr, pte_t *ptep,
> +		struct folio *folio, struct page *first_page, unsigned long addr, pte_t *ptep,
>   		pte_t oldpte, pte_t ptent, int nr_ptes, struct mmu_gather *tlb)
>   {
> -	struct page *first_page = folio_page(folio, 0);
>   	bool expected_anon_exclusive;
>   	int sub_batch_idx = 0;
>   	int len;
>   
>   	while (nr_ptes) {
> -		expected_anon_exclusive = PageAnonExclusive(first_page + sub_batch_idx);
> +		expected_anon_exclusive = PageAnonExclusive(nth_page(first_page, sub_batch_idx));

We shouldn't need nth_page here, for the same reason we don't use it in 
rmap code: we're operating within a single page table and hugetlb does 
not apply.

-- 
Cheers,

David / dhildenb