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

[Qi Zheng]

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?

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

--
Thanks,
Qi