Re: [PATCH -next] uprobes: fix two zero old_folio bugs in __replace_page()

[Oleg Nesterov]

Can't comment, my understanding of mm/ is not enough these days.

Just one question...

On 02/17, Tong Tiangen wrote:
>
> Fixes: 7396fa818d62 ("uprobes/core: Make background page replacement logic account for rss_stat counters")
> Fixes: 2b1444983508 ("uprobes, mm, x86: Add the ability to install and remove uprobes breakpoints")

Are you sure this logic was wrong from the very beginning? Just curious.

Oleg.

> Signed-off-by: Tong Tiangen <tongtiangen@xxxxxxxxxx>
> ---
>  kernel/events/uprobes.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 46ddf3a2334d..ff5694acfa68 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -213,7 +213,8 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>  		dec_mm_counter(mm, MM_ANONPAGES);
>  
>  	if (!folio_test_anon(old_folio)) {
> -		dec_mm_counter(mm, mm_counter_file(old_folio));
> +		if (!is_zero_folio(old_folio))
> +			dec_mm_counter(mm, mm_counter_file(old_folio));
>  		inc_mm_counter(mm, MM_ANONPAGES);
>  	}
>  
> @@ -227,7 +228,8 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>  	if (!folio_mapped(old_folio))
>  		folio_free_swap(old_folio);
>  	page_vma_mapped_walk_done(&pvmw);
> -	folio_put(old_folio);
> +	if (!is_zero_folio(old_folio))
> +		folio_put(old_folio);
>  
>  	err = 0;
>   unlock:
> -- 
> 2.25.1
>