| Message ID | 20210420133048.6773-4-linmiaohe@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | close various race windows for swap | expand |
Miaohe Lin <linmiaohe@huawei.com> writes: > The non_swap_entry() was used for working with VMA based swap readahead > via commit ec560175c0b6 ("mm, swap: VMA based swap readahead"). At that time, the non_swap_entry() checking is necessary because the function is called before checking that in do_swap_page(). > Then it's > moved to swap_ra_info() since commit eaf649ebc3ac ("mm: swap: clean up swap > readahead"). After that, the non_swap_entry() checking is unnecessary, because swap_ra_info() is called after non_swap_entry() has been checked already. The resulting code is confusing. > But this makes the code confusing. The non_swap_entry() check > looks racy because while we released the pte lock, somebody else might have > faulted in this pte. So we should check whether it's swap pte first to > guard against such race or swap_type will be unexpected. The race isn't important because it will not cause problem. Best Regards, Huang, Ying > But the swap_entry > isn't used in this function and we will have enough checking when we really > operate the PTE entries later. So checking for non_swap_entry() is not > really needed here and should be removed to avoid confusion. > > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > --- > mm/swap_state.c | 6 ------ > 1 file changed, 6 deletions(-) > > diff --git a/mm/swap_state.c b/mm/swap_state.c > index 272ea2108c9d..df5405384520 100644 > --- a/mm/swap_state.c > +++ b/mm/swap_state.c > @@ -721,7 +721,6 @@ static void swap_ra_info(struct vm_fault *vmf, > { > struct vm_area_struct *vma = vmf->vma; > unsigned long ra_val; > - swp_entry_t entry; > unsigned long faddr, pfn, fpfn; > unsigned long start, end; > pte_t *pte, *orig_pte; > @@ -739,11 +738,6 @@ 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)))) { > - pte_unmap(orig_pte); > - return; > - } > > fpfn = PFN_DOWN(faddr); > ra_val = GET_SWAP_RA_VAL(vma);
diff --git a/mm/swap_state.c b/mm/swap_state.c index 272ea2108c9d..df5405384520 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -721,7 +721,6 @@ static void swap_ra_info(struct vm_fault *vmf, { struct vm_area_struct *vma = vmf->vma; unsigned long ra_val; - swp_entry_t entry; unsigned long faddr, pfn, fpfn; unsigned long start, end; pte_t *pte, *orig_pte; @@ -739,11 +738,6 @@ 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)))) { - pte_unmap(orig_pte); - return; - } fpfn = PFN_DOWN(faddr); ra_val = GET_SWAP_RA_VAL(vma);
The non_swap_entry() was used for working with VMA based swap readahead via commit ec560175c0b6 ("mm, swap: VMA based swap readahead"). Then it's moved to swap_ra_info() since commit eaf649ebc3ac ("mm: swap: clean up swap readahead"). But this makes the code confusing. The non_swap_entry() check looks racy because while we released the pte lock, somebody else might have faulted in this pte. So we should check whether it's swap pte first to guard against such race or swap_type will be unexpected. But the swap_entry isn't used in this function and we will have enough checking when we really operate the PTE entries later. So checking for non_swap_entry() is not really needed here and should be removed to avoid confusion. Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- mm/swap_state.c | 6 ------ 1 file changed, 6 deletions(-)