Commit 59bf4fb9 authored Jan 15, 2016 by Toshi Kani Committed by Linus Torvalds Jan 15, 2016

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 <toshi.kani@hpe.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@linux.intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 01871e59

fs/dax.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -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;