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, 4 insertions, 4 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 56432ff8d4e3..70789df7dab4 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -29,8 +29,9 @@ struct mm_struct;
 
 extern void mm_init_cgroup(struct mm_struct *mm, struct task_struct *p);
 extern void mm_free_cgroup(struct mm_struct *mm);
-extern void page_assign_page_cgroup(struct page *page,
-					struct page_cgroup *pc);
+
+#define page_reset_bad_cgroup(page)	((page)->page_cgroup = 0)
+
 extern struct page_cgroup *page_get_page_cgroup(struct page *page);
 extern int mem_cgroup_charge(struct page *page, struct mm_struct *mm,
 				gfp_t gfp_mask);
@@ -82,8 +83,7 @@ static inline void mm_free_cgroup(struct mm_struct *mm)
 {
 }
 
-static inline void page_assign_page_cgroup(struct page *page,
-						struct page_cgroup *pc)
+static inline void page_reset_bad_cgroup(struct page *page)
 {
 }