On Mon, 2015-11-23 at 12:45 -0800, Dan Williams wrote: > On Mon, Nov 23, 2015 at 12:05 PM, Toshi Kani <toshi.kani@xxxxxxx> wrote: > > An infinite loop of PMD faults was observed when attempted to > > mlock() a private read-only PMD mmap'd range of a DAX file. > > > > __dax_pmd_fault() simply returns with VM_FAULT_FALLBACK when > > falling back to PTE on COW. However, __handle_mm_fault() > > returns without falling back to handle_pte_fault() because > > a PMD map is present in this case. > > > > Change __dax_pmd_fault() to split the PMD map, if present, > > before returning with VM_FAULT_FALLBACK. > > > > Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx> > > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > > Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxxxx> > > Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> > > I thought the patch from Ross already addressed the infinite loop: > > https://patchwork.kernel.org/patch/7653731/ This fixes a different issue. I hit this one while testing my other patch along with the Ross's patch. > > --- > > fs/dax.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/fs/dax.c b/fs/dax.c > > index 43671b6..3405583 100644 > > --- a/fs/dax.c > > +++ b/fs/dax.c > > @@ -546,8 +546,10 @@ int __dax_pmd_fault(struct vm_area_struct *vma, > > unsigned long address, > > return VM_FAULT_FALLBACK; > > > > /* Fall back to PTEs if we're going to COW */ > > - if (write && !(vma->vm_flags & VM_SHARED)) > > + if (write && !(vma->vm_flags & VM_SHARED)) { > > + split_huge_page_pmd(vma, address, pmd); > > return VM_FAULT_FALLBACK; > > + } > > /* If the PMD would extend outside the VMA */ > > if (pmd_addr < vma->vm_start) > > return VM_FAULT_FALLBACK; > > This is a nop if CONFIG_TRANSPARENT_HUGEPAGE=n, so I don't think it's > a complete fix. Well, __dax_pmd_fault() itself depends on CONFIG_TRANSPARENT_HUGEPAGE. 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>