From: Toshi Kani <toshi.kani@hpe.com>
Date: Sat, 16 Jan 2016 00:56:05 +0000 (-0800)
Subject: dax: Split pmd map when fallback on COW
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=59bf4fb9d386601cbaa70a9b00159abb846dedaa;p=linux-beck.git

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>
---

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;