On Mon, 2015-11-30 at 14:08 -0800, Dan Williams wrote: > On Mon, Nov 23, 2015 at 12:04 PM, Toshi Kani <toshi.kani@xxxxxxx> wrote: > > The following oops was observed when mmap() with MAP_POPULATE > > pre-faulted pmd mappings of a DAX file. follow_trans_huge_pmd() > > expects that a target address has a struct page. > > > > BUG: unable to handle kernel paging request at ffffea0012220000 > > follow_trans_huge_pmd+0xba/0x390 > > follow_page_mask+0x33d/0x420 > > __get_user_pages+0xdc/0x800 > > populate_vma_page_range+0xb5/0xe0 > > __mm_populate+0xc5/0x150 > > vm_mmap_pgoff+0xd5/0xe0 > > SyS_mmap_pgoff+0x1c1/0x290 > > SyS_mmap+0x1b/0x30 > > > > Fix it by making the PMD pre-fault handling consistent with PTE. > > After pre-faulted in faultin_page(), follow_page_mask() calls > > follow_trans_huge_pmd(), which is changed to call follow_pfn_pmd() > > for VM_PFNMAP or VM_MIXEDMAP. follow_pfn_pmd() handles FOLL_TOUCH > > and returns with -EEXIST. > > > > Reported-by: Mauricio Porto <mauricio.porto@xxxxxxx> > > Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxxxx> > > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > > Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> > > --- > > Hey Toshi, > > I ended up fixing this differently with follow_pmd_devmap() introduced > in this series: > > https://lists.01.org/pipermail/linux-nvdimm/2015-November/003033.html > > Does the latest libnvdimm-pending branch [1] pass your test case? Hi Dan, I ran several test cases, and they all hit the case "pfn not in memmap" in __dax_pmd_fault() during mmap(MAP_POPULATE). Looking at the dax.pfn, PFN_DEV is set but PFN_MAP is not. I have not looked into why, but I thought I let you know first. I've also seen the test thread got hung up at the end sometime. I also noticed that reason is not set in the case below. if (length < PMD_SIZE || (pfn_t_to_pfn(dax.pfn) & PG_PMD_COLOUR)) { dax_unmap_atomic(bdev, &dax); goto fallback; } Thanks, -Toshi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>