Re: [PATCH] mm: Fix warning in insert_pfn()

[Dan Williams <dan.j.williams@intel.com>]

On Wed, Oct 3, 2018 at 9:40 AM Theodore Y. Ts'o <tytso@mit.edu> wrote:
>
> On Fri, Aug 24, 2018 at 05:45:42PM +0200, Jan Kara wrote:
> > In DAX mode a write pagefault can race with write(2) in the following
> > way:
> >
> > CPU0                            CPU1
> >                                 write fault for mapped zero page (hole)
> > dax_iomap_rw()
> >   iomap_apply()
> >     xfs_file_iomap_begin()
> >       - allocates blocks
> >     dax_iomap_actor()
> >       invalidate_inode_pages2_range()
> >         - invalidates radix tree entries in given range
> >                                 dax_iomap_pte_fault()
> >                                   grab_mapping_entry()
> >                                     - no entry found, creates empty
> >                                   ...
> >                                   xfs_file_iomap_begin()
> >                                     - finds already allocated block
> >                                   ...
> >                                   vmf_insert_mixed_mkwrite()
> >                                     - WARNs and does nothing because there
> >                                       is still zero page mapped in PTE
> >         unmap_mapping_pages()
> >
> > This race results in WARN_ON from insert_pfn() and is occasionally
> > triggered by fstest generic/344. Note that the race is otherwise
> > harmless as before write(2) on CPU0 is finished, we will invalidate page
> > tables properly and thus user of mmap will see modified data from
> > write(2) from that point on. So just restrict the warning only to the
> > case when the PFN in PTE is not zero page.
> >
> > Signed-off-by: Jan Kara <jack@suse.cz>
>
> I don't see this in linux-next.  What's the status of this patch?
>

It's in Andrew's tree. I believe we are awaiting the next -next
release to rebase on latest mmotm.