memcg: bad page if page_cgroup when free

Replace free_hot_cold_page's VM_BUG_ON(page_get_page_cgroup(page)) by a "Bad
page state" and clear: most users don't have CONFIG_DEBUG_VM on, and if it
were set here, it'd likely cause corruption when the page is reused.

Don't use page_assign_page_cgroup to clear it: that should be private to
memcontrol.c, and always called with the lock taken; and memmap_init_zone
doesn't need it either - like page->mapping and other pointers throughout the
kernel, Linux assumes pointers in zeroed structures are NULL pointers.

Instead use page_reset_bad_cgroup, added to memcontrol.h for this only.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: David Rientjes <rientjes@google.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hirokazu Takahashi <taka@valinux.co.jp>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 15 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index afdd406f618a..9e170d3c71e5 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -140,11 +140,17 @@ struct mem_cgroup {
 
 /*
  * We use the lower bit of the page->page_cgroup pointer as a bit spin
- * lock. We need to ensure that page->page_cgroup is atleast two
- * byte aligned (based on comments from Nick Piggin)
+ * lock.  We need to ensure that page->page_cgroup is at least two
+ * byte aligned (based on comments from Nick Piggin).  But since
+ * bit_spin_lock doesn't actually set that lock bit in a non-debug
+ * uniprocessor kernel, we should avoid setting it here too.
  */
 #define PAGE_CGROUP_LOCK_BIT    0x0
-#define PAGE_CGROUP_LOCK                (1 << PAGE_CGROUP_LOCK_BIT)
+#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
+#define PAGE_CGROUP_LOCK        (1 << PAGE_CGROUP_LOCK_BIT)
+#else
+#define PAGE_CGROUP_LOCK        0x0
+#endif
 
 /*
  * A page_cgroup page is associated with every page descriptor. The
@@ -271,19 +277,10 @@ static inline int page_cgroup_locked(struct page *page)
                                         &page->page_cgroup);
 }
 
-void page_assign_page_cgroup(struct page *page, struct page_cgroup *pc)
+static void page_assign_page_cgroup(struct page *page, struct page_cgroup *pc)
 {
-        int locked;
-
-        /*
-         * While resetting the page_cgroup we might not hold the
-         * page_cgroup lock. free_hot_cold_page() is an example
-         * of such a scenario
-         */
-        if (pc)
-                VM_BUG_ON(!page_cgroup_locked(page));
-        locked = (page->page_cgroup & PAGE_CGROUP_LOCK);
-        page->page_cgroup = ((unsigned long)pc | locked);
+        VM_BUG_ON(!page_cgroup_locked(page));
+        page->page_cgroup = ((unsigned long)pc | PAGE_CGROUP_LOCK);
 }
 
 struct page_cgroup *page_get_page_cgroup(struct page *page)