Kairui Song <ryncsn@xxxxxxxxx> writes:
> From: Kairui Song <kasong@xxxxxxxxxxx>
>
> Convert a volatile variable to more readable READ_ONCE. And this
> actually avoids the code from reading the variable twice redundantly
> when it races.
>
> Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
LGTM, Thanks!
Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> ---
> mm/swapfile.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 72e481aacd5d..ff4f3cb85232 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1836,13 +1836,13 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
> pte_t *pte;
> struct swap_info_struct *si;
> int ret = 0;
> - volatile unsigned char *swap_map;
>
> si = swap_info[type];
> pte = pte_offset_map(pmd, addr);
> do {
> struct folio *folio;
> unsigned long offset;
> + unsigned char swp_count;
>
> if (!is_swap_pte(*pte))
> continue;
> @@ -1853,7 +1853,6 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
>
> offset = swp_offset(entry);
> pte_unmap(pte);
> - swap_map = &si->swap_map[offset];
> folio = swap_cache_get_folio(entry, vma, addr);
> if (!folio) {
> struct page *page;
> @@ -1870,8 +1869,10 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
> folio = page_folio(page);
> }
> if (!folio) {
> - if (*swap_map == 0 || *swap_map == SWAP_MAP_BAD)
> + swp_count = READ_ONCE(si->swap_map[offset]);
> + if (swp_count == 0 || swp_count == SWAP_MAP_BAD)
> goto try_next;
> +
> return -ENOMEM;
> }
