On Wed, Sep 16, 2015 at 02:12:18PM +0300, Kirill A. Shutemov wrote:
> On Tue, Sep 15, 2015 at 04:52:42PM -0700, Dan Williams wrote:
> > Hi Kirill,
> >
> > On Fri, Aug 7, 2015 at 4:53 AM, Kirill A. Shutemov
> > <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> > > DAX is not so special: we need i_mmap_lock to protect mapping->i_mmap.
> > >
> > > __dax_pmd_fault() uses unmap_mapping_range() shoot out zero page from
> > > all mappings. We need to drop i_mmap_lock there to avoid lock deadlock.
> > >
> > > Re-aquiring the lock should be fine since we check i_size after the
> > > point.
> > >
> > > Not-yet-signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
> > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > > ---
> > > fs/dax.c | 35 +++++++++++++++++++----------------
> > > mm/memory.c | 11 ++---------
> > > 2 files changed, 21 insertions(+), 25 deletions(-)
> > >
> > > diff --git a/fs/dax.c b/fs/dax.c
> > > index 9ef9b80cc132..ed54efedade6 100644
> > > --- a/fs/dax.c
> > > +++ b/fs/dax.c
> > > @@ -554,6 +554,25 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
> > > if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE)
> > > goto fallback;
> > >
> > > + if (buffer_unwritten(&bh) || buffer_new(&bh)) {
> > > + int i;
> > > + for (i = 0; i < PTRS_PER_PMD; i++)
> > > + clear_page(kaddr + i * PAGE_SIZE);
> >
> > This patch, now upstream as commit 46c043ede471, moves the call to
> > clear_page() earlier in __dax_pmd_fault(). However, 'kaddr' is not
> > set at this point, so I'm not sure this path was ever tested.
>
> Ughh. It's obviously broken.
>
> I took fs/dax.c part of the patch from Matthew. And I'm not sure now we
> would need to move this "if (buffer_unwritten(&bh) || buffer_new(&bh)) {"
> block around. It should work fine where it was before. Right?
> Matthew?
Moving the "if (buffer_unwritten(&bh) || buffer_new(&bh)) {" block back seems
correct to me. Matthew is out for a while, so we should probably take care of
this without him.
Kirill, do you want to whip up a quick patch? I'm happy to do it if you're
busy.
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