From 59bf4fb9d386601cbaa70a9b00159abb846dedaa Mon Sep 17 00:00:00 2001 From: Toshi Kani Date: Fri, 15 Jan 2016 16:56:05 -0800 Subject: [PATCH] dax: Split pmd map when fallback on COW 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 Signed-off-by: Dan Williams Cc: Kirill A. Shutemov Cc: Matthew Wilcox Cc: Ross Zwisler Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/dax.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/dax.c b/fs/dax.c index 5c548d821a2a..3220da70ee20 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -578,8 +578,10 @@ 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_pmd(vma, pmd, address); return VM_FAULT_FALLBACK; + } /* If the PMD would extend outside the VMA */ if (pmd_addr < vma->vm_start) return VM_FAULT_FALLBACK;