Re: [PATCH] mm/hugetlb: avoid corrupting page->mapping in hugetlb_mcopy_atomic_pte

[Andrew Morton]

On Tue, 12 Jul 2022 21:05:42 +0800 Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:

> In MCOPY_ATOMIC_CONTINUE case with a non-shared VMA, pages in the page
> cache are installed in the ptes. But hugepage_add_new_anon_rmap is called
> for them mistakenly because they're not vm_shared. This will corrupt the
> page->mapping used by page cache code.

Well that sounds bad.  And theories on why this has gone unnoticed for
over a year?  I assume this doesn't have coverage in our selftests?

> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6038,7 +6038,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
>  	if (!huge_pte_none_mostly(huge_ptep_get(dst_pte)))
>  		goto out_release_unlock;
>  
> -	if (vm_shared) {
> +	if (page_in_pagecache) {
>  		page_dup_file_rmap(page, true);
>  	} else {
>  		ClearHPageRestoreReserve(page);
> -- 
> 2.23.0