Re: [PATCH v3 1/4] mm: update the memmap stat before page is freed

[Fan Ni]

On Thu, Aug 08, 2024 at 03:42:34PM +0000, Pasha Tatashin wrote:
> It is more logical to update the stat before the page is freed, to avoid
> use after free scenarios.
> 
> Fixes: 15995a352474 ("mm: report per-page metadata information")
> Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

Reviewed-by: Fan Ni <fan.ni@xxxxxxxxxxx>

> ---
>  mm/hugetlb_vmemmap.c | 4 ++--
>  mm/page_ext.c        | 8 ++++----
>  2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 829112b0a914..fa83a7b38199 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -185,11 +185,11 @@ static int vmemmap_remap_range(unsigned long start, unsigned long end,
>  static inline void free_vmemmap_page(struct page *page)
>  {
>  	if (PageReserved(page)) {
> -		free_bootmem_page(page);
>  		mod_node_page_state(page_pgdat(page), NR_MEMMAP_BOOT, -1);
> +		free_bootmem_page(page);
>  	} else {
> -		__free_page(page);
>  		mod_node_page_state(page_pgdat(page), NR_MEMMAP, -1);
> +		__free_page(page);
>  	}
>  }
>  
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index c191e490c401..962d45eee1f8 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -330,18 +330,18 @@ static void free_page_ext(void *addr)
>  	if (is_vmalloc_addr(addr)) {
>  		page = vmalloc_to_page(addr);
>  		pgdat = page_pgdat(page);
> +		mod_node_page_state(pgdat, NR_MEMMAP,
> +				    -1L * (DIV_ROUND_UP(table_size, PAGE_SIZE)));
>  		vfree(addr);
>  	} else {
>  		page = virt_to_page(addr);
>  		pgdat = page_pgdat(page);
> +		mod_node_page_state(pgdat, NR_MEMMAP,
> +				    -1L * (DIV_ROUND_UP(table_size, PAGE_SIZE)));
>  		BUG_ON(PageReserved(page));
>  		kmemleak_free(addr);
>  		free_pages_exact(addr, table_size);
>  	}
> -
> -	mod_node_page_state(pgdat, NR_MEMMAP,
> -			    -1L * (DIV_ROUND_UP(table_size, PAGE_SIZE)));
> -
>  }
>  
>  static void __free_page_ext(unsigned long pfn)
> -- 
> 2.46.0.76.ge559c4bf1a-goog
>