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dax: Split pmd map when fallback on COW

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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>
This commit is contained in:
Toshi Kani 2016-01-15 16:56:05 -08:00 committed by Linus Torvalds
parent 01871e59af
commit 59bf4fb9d3
1 changed files with 3 additions and 1 deletions
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4
fs/dax.c
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@ -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;