Re: [PATCH] shmem: Update folio if shmem_replace_page() updates the page

[Andrew Morton]

On Sat, 30 Jul 2022 05:25:18 +0100 "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> wrote:

> If we allocate a new page, we need to make sure that our folio matches
> that new page.  This will be solved by changing shmem_replace_page()
> to shmem_replace_folio(), but this is the minimal fix.
> 
> ...
>
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1771,6 +1771,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
>  
>  	if (shmem_should_replace_folio(folio, gfp)) {
>  		error = shmem_replace_page(&page, gfp, info, index);
> +		folio = page_folio(page);
>  		if (error)
>  			goto failed;
>  	}

What are the user-visible runtime effects of the bug?

Should we backport this into 5.19.X?