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? Thanks, - Ted
