On Wed, Oct 3, 2018 at 9:40 AM Theodore Y. Ts'o <tytso@xxxxxxx> 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@xxxxxxx> > > 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.
