Re: [PATCH 3/5] mm/swap_state: fix get_shadow_from_swap_cache() race with swapoff

[Huang, Ying]

Miaohe Lin <linmiaohe@xxxxxxxxxx> writes:

> The function get_shadow_from_swap_cache() can race with swapoff, though
> it's only called by do_swap_page() now.
>
> Fixes: aae466b0052e ("mm/swap: implement workingset detection for anonymous LRU")
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>

This is unnecessary.  The only caller has guaranteed the swap device
from swapoff.

Best Regards,
Huang, Ying

> ---
>  mm/swap_state.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 272ea2108c9d..709c260d644a 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -83,11 +83,14 @@ void show_swap_cache_info(void)
>  
>  void *get_shadow_from_swap_cache(swp_entry_t entry)
>  {
> -	struct address_space *address_space = swap_address_space(entry);
> -	pgoff_t idx = swp_offset(entry);
> +	struct swap_info_struct *si;
>  	struct page *page;
>  
> -	page = xa_load(&address_space->i_pages, idx);
> +	si = get_swap_device(entry);
> +	if (!si)
> +		return NULL;
> +	page = xa_load(&swap_address_space(entry)->i_pages, swp_offset(entry));
> +	put_swap_device(si);
>  	if (xa_is_value(page))
>  		return page;
>  	return NULL;