On Wed, Oct 19, 2016 at 09:16:00AM +0200, Jan Kara wrote:
> On Tue 18-10-16 12:35:25, Ross Zwisler wrote:
> > 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 <jack@xxxxxxx>
> > > ---
> > > 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
>
> Fixed, thanks.
>
> > > @@ -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)) {
>
> Right, finish_mkwrite_fault() cannot currently throw other errors than
> "retry needed" which is indicated by tmp == 0. However I'd prefer to keep
> symmetry with finish_fault() handler which can throw other errors and
> better be prepared to handle them from finish_mkwrite_fault() as well.
Fair enough. You can add:
Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
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