1 files changed, 21 insertions, 6 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index 0b714747c028..2a0ea3ef509e 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -543,7 +543,7 @@ static int move_to_new_page(struct page *newpage, struct page *page)
  * to the newly allocated page in newpage.
  */
 static int unmap_and_move(new_page_t get_new_page, unsigned long private,
-                        struct page *page, int force)
+                        struct page *page, int force, int offlining)
 {
         int rc = 0;
         int *result = NULL;
@@ -569,6 +569,20 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
                 lock_page(page);
         }
 
+        /*
+         * Only memory hotplug's offline_pages() caller has locked out KSM,
+         * and can safely migrate a KSM page.  The other cases have skipped
+         * PageKsm along with PageReserved - but it is only now when we have
+         * the page lock that we can be certain it will not go KSM beneath us
+         * (KSM will not upgrade a page from PageAnon to PageKsm when it sees
+         * its pagecount raised, but only here do we take the page lock which
+         * serializes that).
+         */
+        if (PageKsm(page) && !offlining) {
+                rc = -EBUSY;
+                goto unlock;
+        }
+
         /* charge against new page */
         charge = mem_cgroup_prepare_migration(page, &mem);
         if (charge == -ENOMEM) {
@@ -685,7 +699,7 @@ move_newpage:
  * Return: Number of pages not migrated or error code.
  */
 int migrate_pages(struct list_head *from,
-                new_page_t get_new_page, unsigned long private)
+                new_page_t get_new_page, unsigned long private, int offlining)
 {
         int retry = 1;
         int nr_failed = 0;
@@ -705,7 +719,7 @@ int migrate_pages(struct list_head *from,
                         cond_resched();
 
                         rc = unmap_and_move(get_new_page, private,
-                                                page, pass > 2);
+                                                page, pass > 2, offlining);
 
                         switch(rc) {
                         case -ENOMEM:
@@ -801,7 +815,8 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
                 if (!page)
                         goto set_status;
 
-                if (PageReserved(page))         /* Check for zero page */
+                /* Use PageReserved to check for zero page */
+                if (PageReserved(page) || PageKsm(page))
                         goto put_and_set;
 
                 pp->page = page;
@@ -838,7 +853,7 @@ set_status:
         err = 0;
         if (!list_empty(&pagelist))
                 err = migrate_pages(&pagelist, new_page_node,
-                                (unsigned long)pm);
+                                (unsigned long)pm, 0);
 
         up_read(&mm->mmap_sem);
         return err;
@@ -959,7 +974,7 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
 
                 err = -ENOENT;
                 /* Use PageReserved to check for zero page */
-                if (!page || PageReserved(page))
+                if (!page || PageReserved(page) || PageKsm(page))
                         goto set_status;
 
                 err = page_to_nid(page);