mm/rmap: factor lock function out of rmap_walk_anon()

When we traverse anon_vma, we need to take a read-side anon_lock.  But
there is subtle difference in the situation so that we can't use same
method to take a lock in each cases.  Therefore, we need to make
rmap_walk_anon() taking difference lock function.

This patch is the first step, factoring lock function for anon_lock out
of rmap_walk_anon().  It will be used in case of removing migration
entry and in default of rmap_walk_anon().

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 20 insertions, 8 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 7eab4ed304c1..5a79bf585e27 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1684,6 +1684,24 @@ void __put_anon_vma(struct anon_vma *anon_vma)
 }
 
 #ifdef CONFIG_MIGRATION
+static struct anon_vma *rmap_walk_anon_lock(struct page *page)
+{
+        struct anon_vma *anon_vma;
+
+        /*
+         * Note: remove_migration_ptes() cannot use page_lock_anon_vma_read()
+         * because that depends on page_mapped(); but not all its usages
+         * are holding mmap_sem. Users without mmap_sem are required to
+         * take a reference count to prevent the anon_vma disappearing
+         */
+        anon_vma = page_anon_vma(page);
+        if (!anon_vma)
+                return NULL;
+
+        anon_vma_lock_read(anon_vma);
+        return anon_vma;
+}
+
 /*
  * rmap_walk() and its helpers rmap_walk_anon() and rmap_walk_file():
  * Called by migrate.c to remove migration ptes, but might be used more later.
@@ -1696,16 +1714,10 @@ static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *,
         struct anon_vma_chain *avc;
         int ret = SWAP_AGAIN;
 
-        /*
-         * Note: remove_migration_ptes() cannot use page_lock_anon_vma_read()
-         * because that depends on page_mapped(); but not all its usages
-         * are holding mmap_sem. Users without mmap_sem are required to
-         * take a reference count to prevent the anon_vma disappearing
-         */
-        anon_vma = page_anon_vma(page);
+        anon_vma = rmap_walk_anon_lock(page);
         if (!anon_vma)
                 return ret;
-        anon_vma_lock_read(anon_vma);
+
         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
                 struct vm_area_struct *vma = avc->vma;
                 unsigned long address = vma_address(page, vma);