Miaohe Lin <linmiaohe@xxxxxxxxxx> writes:
> While we released the pte lock, somebody else might faulted in this pte.
> So we should check whether it's swap pte first to guard against such race
> or swp_type would be unexpected. And we can also avoid some unnecessary
> readahead cpu cycles possibly.
>
> Fixes: ec560175c0b6 ("mm, swap: VMA based swap readahead")
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> ---
> mm/swap_state.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 709c260d644a..3bf0d0c297bc 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -724,10 +724,10 @@ static void swap_ra_info(struct vm_fault *vmf,
> {
> struct vm_area_struct *vma = vmf->vma;
> unsigned long ra_val;
> - swp_entry_t entry;
> + swp_entry_t swap_entry;
> unsigned long faddr, pfn, fpfn;
> unsigned long start, end;
> - pte_t *pte, *orig_pte;
> + pte_t *pte, *orig_pte, entry;
> unsigned int max_win, hits, prev_win, win, left;
> #ifndef CONFIG_64BIT
> pte_t *tpte;
> @@ -742,8 +742,13 @@ static void swap_ra_info(struct vm_fault *vmf,
>
> faddr = vmf->address;
> orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
> - entry = pte_to_swp_entry(*pte);
> - if ((unlikely(non_swap_entry(entry)))) {
> + entry = *pte;
> + if (unlikely(!is_swap_pte(entry))) {
> + pte_unmap(orig_pte);
> + return;
> + }
> + swap_entry = pte_to_swp_entry(entry);
> + if ((unlikely(non_swap_entry(swap_entry)))) {
> pte_unmap(orig_pte);
> return;
> }
This isn't a real issue. entry or swap_entry isn't used in this
function. And we have enough checking when we really operate the PTE
entries later. But I admit it's confusing. So I suggest to just remove
the checking. We will check it when necessary.
Best Regards,
Huang, Ying
