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

[Hugh Dickins]

On Sat, 30 Jul 2022, Matthew Wilcox (Oracle) 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.
> 
> Fixes: da08e9b79323 ("mm/shmem: convert shmem_swapin_page() to shmem_swapin_folio()")
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>

Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>

I hit this myself just once, at about the very time you sent the fix.
But, thinking that shmem_replace_page() was special for gma500, couldn't
understand how I (or most people) would ever get there.  Turns out that
nowadays tmpfs symlinks longer than 128 can come this way on 32-bit (I
had been testing kmap_local stuff for other reasons).

And today I see that Zdenek hit it on 5.19-rc back in June:
https://lore.kernel.org/lkml/584ae788-05e3-5824-8c85-cbb833677850@xxxxxxxxxx/
so this patch is definitely one for -stable.

Hugh

> ---
>  mm/shmem.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index a6f565308133..bcc0a3c7b5bf 100644
> --- 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;
>  	}
> -- 
> 2.35.1