revert "mm: mempolicy: Let vma_merge and vma_split handle vma->vm_policy linkages"

Commit 05f144a0d5c2 ("mm: mempolicy: Let vma_merge and vma_split handle
vma->vm_policy linkages") removed vma->vm_policy updates code but it is
the purpose of mbind_range().  Now, mbind_range() is virtually a no-op
and while it does not allow memory corruption it is not the right fix.
This patch is a revert.

[mgorman@suse.de: Edited changelog]
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: Josh Boyer <jwboyer@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 24 insertions, 17 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 4ada3be6e252..92daa267baf2 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -607,6 +607,27 @@ check_range(struct mm_struct *mm, unsigned long start, unsigned long end,
         return first;
 }
 
+/* Apply policy to a single VMA */
+static int policy_vma(struct vm_area_struct *vma, struct mempolicy *new)
+{
+        int err = 0;
+        struct mempolicy *old = vma->vm_policy;
+
+        pr_debug("vma %lx-%lx/%lx vm_ops %p vm_file %p set_policy %p\n",
+                 vma->vm_start, vma->vm_end, vma->vm_pgoff,
+                 vma->vm_ops, vma->vm_file,
+                 vma->vm_ops ? vma->vm_ops->set_policy : NULL);
+
+        if (vma->vm_ops && vma->vm_ops->set_policy)
+                err = vma->vm_ops->set_policy(vma, new);
+        if (!err) {
+                mpol_get(new);
+                vma->vm_policy = new;
+                mpol_put(old);
+        }
+        return err;
+}
+
 /* Step 2: apply policy to a range and do splits. */
 static int mbind_range(struct mm_struct *mm, unsigned long start,
                        unsigned long end, struct mempolicy *new_pol)
@@ -655,23 +676,9 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
                         if (err)
                                 goto out;
                 }
-
-                /*
-                 * Apply policy to a single VMA. The reference counting of
-                 * policy for vma_policy linkages has already been handled by
-                 * vma_merge and split_vma as necessary. If this is a shared
-                 * policy then ->set_policy will increment the reference count
-                 * for an sp node.
-                 */
-                pr_debug("vma %lx-%lx/%lx vm_ops %p vm_file %p set_policy %p\n",
-                        vma->vm_start, vma->vm_end, vma->vm_pgoff,
-                        vma->vm_ops, vma->vm_file,
-                        vma->vm_ops ? vma->vm_ops->set_policy : NULL);
-                if (vma->vm_ops && vma->vm_ops->set_policy) {
-                        err = vma->vm_ops->set_policy(vma, new_pol);
-                        if (err)
-                                goto out;
-                }
+                err = policy_vma(vma, new_pol);
+                if (err)
+                        goto out;
         }
 
  out: