mm: speculative page references

[firefly-linux-kernel-4.4.55.git] / mm / migrate.c

diff --git a/mm/migrate.c b/mm/migrate.c
index d8c65a65c61d5701b8ecbc9185ac864ef564707c..3ca6392e82cc57ccf5634fd0b27f99fd6556c9d1 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -285,7 +285,15 @@ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
 
        page = migration_entry_to_page(entry);
 
-       get_page(page);
+       /*
+        * Once radix-tree replacement of page migration started, page_count
+        * *must* be zero. And, we don't want to call wait_on_page_locked()
+        * against a page without get_page().
+        * So, we use get_page_unless_zero(), here. Even failed, page fault
+        * will occur again.
+        */
+       if (!get_page_unless_zero(page))
+               goto out;
        pte_unmap_unlock(ptep, ptl);
        wait_on_page_locked(page);
        put_page(page);
@@ -305,6 +313,7 @@ out:
 static int migrate_page_move_mapping(struct address_space *mapping,
                struct page *newpage, struct page *page)
 {
+       int expected_count;
        void **pslot;
 
        if (!mapping) {
@@ -319,12 +328,18 @@ static int migrate_page_move_mapping(struct address_space *mapping,
        pslot = radix_tree_lookup_slot(&mapping->page_tree,
                                        page_index(page));
 
-       if (page_count(page) != 2 + !!PagePrivate(page) ||
+       expected_count = 2 + !!PagePrivate(page);
+       if (page_count(page) != expected_count ||
                        (struct page *)radix_tree_deref_slot(pslot) != page) {
                write_unlock_irq(&mapping->tree_lock);
                return -EAGAIN;
        }
 
+       if (!page_freeze_refs(page, expected_count)) {
+               write_unlock_irq(&mapping->tree_lock);
+               return -EAGAIN;
+       }
+
        /*
         * Now we know that no one else is looking at the page.
         */
@@ -338,6 +353,7 @@ static int migrate_page_move_mapping(struct address_space *mapping,
 
        radix_tree_replace_slot(pslot, newpage);
 
+       page_unfreeze_refs(page, expected_count);
        /*
         * Drop cache reference from old page.
         * We know this isn't the last reference.