On Tue, Sep 27, 2016 at 06:08:20PM +0200, Jan Kara wrote:
> Provide a helper function for finishing write faults due to PTE being
> read-only. The helper will be used by DAX to avoid the need of
> complicating generic MM code with DAX locking specifics.
>
> Signed-off-by: Jan Kara <[email protected]>
> ---
> include/linux/mm.h | 1 +
> mm/memory.c | 65
> +++++++++++++++++++++++++++++++-----------------------
> 2 files changed, 39 insertions(+), 27 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 1055f2ece80d..e5a014be8932 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -617,6 +617,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct
> vm_area_struct *vma)
> int alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
> struct page *page);
> int finish_fault(struct vm_fault *vmf);
> +int finish_mkwrite_fault(struct vm_fault *vmf);
> #endif
>
> /*
> diff --git a/mm/memory.c b/mm/memory.c
> index f49e736d6a36..8c8cb7f2133e 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2266,6 +2266,36 @@ oom:
> return VM_FAULT_OOM;
> }
>
> +/**
> + * finish_mkrite_fault - finish page fault making PTE writeable once the page
finish_mkwrite_fault
> @@ -2315,26 +2335,17 @@ static int wp_page_shared(struct vm_fault *vmf)
> put_page(vmf->page);
> return tmp;
> }
> - /*
> - * Since we dropped the lock we need to revalidate
> - * the PTE as someone else may have changed it. If
> - * they did, we just return, as we can count on the
> - * MMU to tell us if they didn't also make it writable.
> - */
> - vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
> - vmf->address, &vmf->ptl);
> - if (!pte_same(*vmf->pte, vmf->orig_pte)) {
> + tmp = finish_mkwrite_fault(vmf);
> + if (unlikely(!tmp || (tmp &
> + (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {
The 'tmp' return from finish_mkwrite_fault() can only be 0 or VM_FAULT_WRITE.
I think this test should just be
if (unlikely(!tmp)) {
With that and the small spelling fix:
Reviewed-by: Ross Zwisler <[email protected]>
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