memcg: fix GPF when cgroup removal races with last exit

[can-eth-gw-linux.git] / mm / memcontrol.c

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1097d8098f8ce2ade8bc2fad020f8471acc05f39..d0e57a3cda1899c156274d53e49e11be42957f87 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1042,6 +1042,19 @@ struct lruvec *mem_cgroup_lru_add_list(struct zone *zone, struct page *page,
 
        pc = lookup_page_cgroup(page);
        memcg = pc->mem_cgroup;
+
+       /*
+        * Surreptitiously switch any uncharged page to root:
+        * an uncharged page off lru does nothing to secure
+        * its former mem_cgroup from sudden removal.
+        *
+        * Our caller holds lru_lock, and PageCgroupUsed is updated
+        * under page_cgroup lock: between them, they make all uses
+        * of pc->mem_cgroup safe.
+        */
+       if (!PageCgroupUsed(pc) && memcg != root_mem_cgroup)
+               pc->mem_cgroup = memcg = root_mem_cgroup;
+
        mz = page_cgroup_zoneinfo(memcg, page);
        /* compound_order() is stabilized through lru_lock */
        MEM_CGROUP_ZSTAT(mz, lru) += 1 << compound_order(page);
@@ -3029,23 +3042,6 @@ void mem_cgroup_uncharge_end(void)
        batch->memcg = NULL;
 }
 
-/*
- * A function for resetting pc->mem_cgroup for newly allocated pages.
- * This function should be called if the newpage will be added to LRU
- * before start accounting.
- */
-void mem_cgroup_reset_owner(struct page *newpage)
-{
-       struct page_cgroup *pc;
-
-       if (mem_cgroup_disabled())
-               return;
-
-       pc = lookup_page_cgroup(newpage);
-       VM_BUG_ON(PageCgroupUsed(pc));
-       pc->mem_cgroup = root_mem_cgroup;
-}
-
 #ifdef CONFIG_SWAP
 /*
  * called after __delete_from_swap_cache() and drop "page" account.