mm: mempolicy: fix mbind_range() && vma_adjust() interaction

vma_adjust() does vma_set_policy(vma, vma_policy(next)) and this
is doubly wrong:

1. This leaks vma->vm_policy if it is not NULL and not equal to
   next->vm_policy.

   This can happen if vma_merge() expands "area", not prev (case 8).

2. This sets the wrong policy if vma_merge() joins prev and area,
   area is the vma the caller needs to update and it still has the
   old policy.

Revert commit 1444f92c8498 ("mm: merging memory blocks resets
mempolicy") which introduced these problems.

Change mbind_range() to recheck mpol_equal() after vma_merge() to fix
the problem that commit tried to address.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Steven T Hampson <steven.t.hampson@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 6 insertions, 2 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 74310017296e..4baf12e534d1 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -732,7 +732,10 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
                 if (prev) {
                         vma = prev;
                         next = vma->vm_next;
-                        continue;
+                        if (mpol_equal(vma_policy(vma), new_pol))
+                                continue;
+                        /* vma_merge() joined vma && vma->next, case 8 */
+                        goto replace;
                 }
                 if (vma->vm_start != vmstart) {
                         err = split_vma(vma->vm_mm, vma, vmstart, 1);
@@ -744,6 +747,7 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
                         if (err)
                                 goto out;
                 }
+ replace:
                 err = vma_replace_policy(vma, new_pol);
                 if (err)
                         goto out;
diff --git a/mm/mmap.c b/mm/mmap.c
index fbad7b091090..1edbaa3136c3 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -865,7 +865,7 @@ again:			remove_next = 1 + (end > next->vm_end);
                 if (next->anon_vma)
                         anon_vma_merge(vma, next);
                 mm->map_count--;
-                vma_set_policy(vma, vma_policy(next));
+                mpol_put(vma_policy(next));
                 kmem_cache_free(vm_area_cachep, next);
                 /*
                  * In mprotect's case 6 (see comments on vma_merge),