| Message ID | 20210425023806.3537283-4-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 as the non_swap_entry() check > looks racy now 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 race > isn't important because it will not cause problem. We would have enough > checking when we really operate the PTE entries later. So we remove the > non_swap_entry() check here to avoid confusion. > > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> Reviewed-by: "Huang, Ying" <ying.huang@intel.com> Best Regards, Huang, Ying > --- > 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"). 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 as the non_swap_entry() check looks racy now 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 race isn't important because it will not cause problem. We would have enough checking when we really operate the PTE entries later. So we remove the non_swap_entry() check here to avoid confusion. Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- mm/swap_state.c | 6 ------ 1 file changed, 6 deletions(-)