[PATCH] mm/hotplug: fix a drain pcp bug when offline pages

[Xishi Qiu]

__offline_pages()
   start_isolate_page_range()
      set_migratetype_isolate()
         set_pageblock_migratetype() -> this pageblock will be marked as 
MIGRATE_ISOLATE
         move_freepages_block() -> pages in PageBuddy will be moved into 
MIGRATE_ISOLATE list
         drain_all_pages() -> drain PCP
            free_pcppages_bulk()
               mt = get_freepage_migratetype(page); -> PCP's migratetype is not 
MIGRATE_ISOLATE
               __free_one_page(page, zone, 0, mt); -> so PCP will not be freed 
into into MIGRATE_ISOLATE list

In this case, the PCP may be allocated again, because they are not in 
PageBuddy's MIGRATE_ISOLATE list. This will cause offline_pages failed.

Signed-off-by: Xishi Qiu <qiuxi...@huawei.com>
---
 mm/page_alloc.c     |   10 ++++++----
 mm/page_isolation.c |   15 ++++++++++++++-
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b100255..d873471 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -965,11 +965,13 @@ int move_freepages(struct zone *zone,
                }
 
                order = page_order(page);
-               list_move(&page->lru,
-                         &zone->free_area[order].free_list[migratetype]);
-               set_freepage_migratetype(page, migratetype);
+               if (get_freepage_migratetype(page) != migratetype) {
+                       list_move(&page->lru,
+                               &zone->free_area[order].free_list[migratetype]);
+                       set_freepage_migratetype(page, migratetype);
+                       pages_moved += 1 << order;
+               }
                page += 1 << order;
-               pages_moved += 1 << order;
        }
 
        return pages_moved;
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 383bdbb..ba1afc9 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -65,8 +65,21 @@ out:
        }
 
        spin_unlock_irqrestore(&zone->lock, flags);
-       if (!ret)
+
+       if (!ret) {
                drain_all_pages();
+               /*
+                * When drain_all_pages() frees cached pages into the buddy
+                * system, it uses the stale migratetype cached in the
+                * page->index field, so try to move free pages to ISOLATE
+                * list again.
+                */
+               spin_lock_irqsave(&zone->lock, flags);
+               nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE);
+               __mod_zone_freepage_state(zone, -nr_pages, migratetype);
+               spin_unlock_irqrestore(&zone->lock, flags);
+       }
+
        return ret;
 }
 
-- 
1.7.1

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