Re: [PATCH -V2 1/5] swap: Remove get/put_swap_device() in __swap_count()

[David Hildenbrand]

On 22.05.23 09:09, Huang Ying wrote:
> __swap_count() is called in do_swap_page() only, which encloses the
> call site with get/put_swap_device() already.
>
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> Cc: Yang Shi <shy828301@xxxxxxxxx>
> Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
> ---
>   mm/swapfile.c | 10 ++--------
>   1 file changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 274bbf797480..8419cba9c192 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1432,16 +1432,10 @@ void swapcache_free_entries(swp_entry_t *entries, int n)
>   
>   int __swap_count(swp_entry_t entry)
>   {
> -	struct swap_info_struct *si;
> +	struct swap_info_struct *si = swp_swap_info(entry);
>   	pgoff_t offset = swp_offset(entry);
> -	int count = 0;
>   
> -	si = get_swap_device(entry);
> -	if (si) {
> -		count = swap_count(si->swap_map[offset]);
> -		put_swap_device(si);
> -	}
> -	return count;
> +	return swap_count(si->swap_map[offset]);
>   }
>   
>   /*

That locking was added in eb085574a752 ("mm, swap: fix race between 
swapoff and some swap operations"). Before 2799e77529c ("swap: fix 
do_swap_page() race with swapoff") added the get_swap_device() to 
do_swap_page().

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

--
Thanks,

David / dhildenb