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.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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