Re: [PATCH 17/31] mm/various: give up if pte_offset_map[_lock]() fails

[Qi Zheng]

On 2023/5/22 20:24, Qi Zheng wrote:
> On 2023/5/22 13:10, Hugh Dickins wrote:
> > Following the examples of nearby code, various functions can just give
> > up if pte_offset_map() or pte_offset_map_lock() fails.  And there's no
> > need for a preliminary pmd_trans_unstable() or other such check, since
> > such cases are now safely handled inside.
> >
> > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> > ---
> >   mm/gup.c            | 9 ++++++---
> >   mm/ksm.c            | 7 ++++---
> >   mm/memcontrol.c     | 8 ++++----
> >   mm/memory-failure.c | 8 +++++---
> >   mm/migrate.c        | 3 +++
> >   mm/swap_state.c     | 3 +++
> >   6 files changed, 25 insertions(+), 13 deletions(-)
>
> [...]
>
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index 3ecb7a40075f..308a56f0b156 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -305,6 +305,9 @@ void migration_entry_wait(struct mm_struct *mm, 
> > pmd_t *pmd,
> >       swp_entry_t entry;
> >       ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
> > +    if (!ptep)
> > +        return;
>
> Maybe we should return false and let the caller handle the failure.
>
> > +
> >       pte = *ptep;
> >       pte_unmap(ptep);
> > diff --git a/mm/swap_state.c b/mm/swap_state.c
> > index b76a65ac28b3..db2ec85ef332 100644
> > --- a/mm/swap_state.c
> > +++ b/mm/swap_state.c
> > @@ -734,6 +734,9 @@ static void swap_ra_info(struct vm_fault *vmf,
> >       /* Copy the PTEs because the page table may be unmapped */
> >       orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
> > +    if (!pte)
> > +        return;
>
> Ditto?

Oh, I see that you handle it in the PATCH[22/31].

> > +
> >       if (fpfn == pfn + 1) {
> >           lpfn = fpfn;
> >           rpfn = fpfn + win;

--
Thanks,
Qi