mm: fix hugepage migration

2.6.37 added an unmap_and_move_huge_page() for memory failure recovery,
but its anon_vma handling was still based around the 2.6.35 conventions.
Update it to use page_lock_anon_vma, get_anon_vma, page_unlock_anon_vma,
drop_anon_vma in the same way as we're now changing unmap_and_move().

I don't particularly like to propose this for stable when I've not seen
its problems in practice nor tested the solution: but it's clearly out of
synch at present.

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Rik van Riel <riel@redhat.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: "Jun'ichi Nomura" <j-nomura@ce.jp.nec.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: <stable@kernel.org> [2.6.37, 2.6.36]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 17 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index a20cf12eded..5b7d1fd2962 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -827,7 +827,6 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
         int rc = 0;
         int *result = NULL;
         struct page *new_hpage = get_new_page(hpage, private, &result);
-        int rcu_locked = 0;
         struct anon_vma *anon_vma = NULL;
 
         if (!new_hpage)
@@ -842,12 +841,10 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
         }
 
         if (PageAnon(hpage)) {
-                rcu_read_lock();
-                rcu_locked = 1;
-
-                if (page_mapped(hpage)) {
-                        anon_vma = page_anon_vma(hpage);
-                        atomic_inc(&anon_vma->external_refcount);
+                anon_vma = page_lock_anon_vma(hpage);
+                if (anon_vma) {
+                        get_anon_vma(anon_vma);
+                        page_unlock_anon_vma(anon_vma);
                 }
         }
 
@@ -859,16 +856,8 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
         if (rc)
                 remove_migration_ptes(hpage, hpage);
 
-        if (anon_vma && atomic_dec_and_lock(&anon_vma->external_refcount,
-                                            &anon_vma->lock)) {
-                int empty = list_empty(&anon_vma->head);
-                spin_unlock(&anon_vma->lock);
-                if (empty)
-                        anon_vma_free(anon_vma);
-        }
-
-        if (rcu_locked)
-                rcu_read_unlock();
+        if (anon_vma)
+                drop_anon_vma(anon_vma);
 out:
         unlock_page(hpage);