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>
---
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;
--
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