Re: [PATCH] mm: fix insert_pfn() return value

Matthew Wilcox
2018-11-27T15:08:56Z

On Tue, Nov 27, 2018 at 02:43:51PM +0000, Mans Rullgard wrote:
> Commit 9b5a8e00d479 ("mm: convert insert_pfn() to vm_fault_t") accidentally
> made insert_pfn() always return an error. Fix this.

Umm. VM_FAULT_NOPAGE is not an error. It's saying "I inserted the PFN,
there's no struct page for the core VM to do anything with". Which is
the correct response from a device driver which has called insert_pfn().

Could you explain a bit more what led you to think there's a problem here?

Also, rather rude of you not to cc the patch author when you claim to
be fixing a bug in their patch.

> Fixes: 9b5a8e00d479 ("mm: convert insert_pfn() to vm_fault_t")
> Signed-off-by: Mans Rullgard <mans@mansr.com>
> ---
> mm/memory.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 4ad2d293ddc2..15baf50e3908 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1524,12 +1524,14 @@ static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
> pfn_t pfn, pgprot_t prot, bool mkwrite)
> {
> struct mm_struct *mm = vma->vm_mm;
> + int retval;
> pte_t *pte, entry;
> spinlock_t *ptl;
>
> pte = get_locked_pte(mm, addr, &ptl);
> if (!pte)
> return VM_FAULT_OOM;
> + retval = VM_FAULT_NOPAGE;
> if (!pte_none(*pte)) {
> if (mkwrite) {
> /*
> @@ -1567,9 +1569,10 @@ static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
> set_pte_at(mm, addr, pte, entry);
> update_mmu_cache(vma, addr, pte); /* XXX: why not for insert_page? */
>
> + retval = 0;
> out_unlock:
> pte_unmap_unlock(pte, ptl);
> - return VM_FAULT_NOPAGE;
> + return retval;
> }
>
> /**
> --
> 2.19.2
>