mm/mempolicy.c: fix pgoff in mbind vma merge

commit 9d8cebd4bcd7 ("mm: fix mbind vma merge problem") didn't really
fix the mbind vma merge problem due to wrong pgoff value passing to
vma_merge(), which made vma_merge() always return NULL.

Before the patch applied, we are getting a result like:

  addr = 0x7fa58f00c000
  [snip]
  7fa58f00c000-7fa58f00d000 rw-p 00000000 00:00 0
  7fa58f00d000-7fa58f00e000 rw-p 00000000 00:00 0
  7fa58f00e000-7fa58f00f000 rw-p 00000000 00:00 0

here 7fa58f00c000->7fa58f00f000 we get 3 VMAs which are expected to be
merged described as described in commit 9d8cebd.

Re-testing the patched kernel with the reproducer provided in commit
9d8cebd, we get the correct result:

  addr = 0x7ffa5aaa2000
  [snip]
  7ffa5aaa2000-7ffa5aaa6000 rw-p 00000000 00:00 0
  7fffd556f000-7fffd5584000 rw-p 00000000 00:00 0                          [stack]

Signed-off-by: Caspar Zhang <caspar@casparzhang.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 3 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 8b57173c1dd5..b1f70d6eec35 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -636,7 +636,6 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
         struct vm_area_struct *prev;
         struct vm_area_struct *vma;
         int err = 0;
-        pgoff_t pgoff;
         unsigned long vmstart;
         unsigned long vmend;
 
@@ -649,9 +648,9 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
                 vmstart = max(start, vma->vm_start);
                 vmend   = min(end, vma->vm_end);
 
-                pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
                 prev = vma_merge(mm, prev, vmstart, vmend, vma->vm_flags,
-                                  vma->anon_vma, vma->vm_file, pgoff, new_pol);
+                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
+                                  new_pol);
                 if (prev) {
                         vma = prev;
                         next = vma->vm_next;