1 files changed, 40 insertions, 1 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f1a0ae6e11b8..bf5e89457149 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2694,7 +2694,10 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
                 goto bypass;
 
         if (unlikely(task_in_memcg_oom(current)))
-                goto bypass;
+                goto nomem;
+
+        if (gfp_mask & __GFP_NOFAIL)
+                oom = false;
 
         /*
          * We always charge the cgroup the mm_struct belongs to.
@@ -6352,6 +6355,42 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
 static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
 {
         struct mem_cgroup *memcg = mem_cgroup_from_css(css);
+        /*
+         * XXX: css_offline() would be where we should reparent all
+         * memory to prepare the cgroup for destruction.  However,
+         * memcg does not do css_tryget() and res_counter charging
+         * under the same RCU lock region, which means that charging
+         * could race with offlining.  Offlining only happens to
+         * cgroups with no tasks in them but charges can show up
+         * without any tasks from the swapin path when the target
+         * memcg is looked up from the swapout record and not from the
+         * current task as it usually is.  A race like this can leak
+         * charges and put pages with stale cgroup pointers into
+         * circulation:
+         *
+         * #0                        #1
+         *                           lookup_swap_cgroup_id()
+         *                           rcu_read_lock()
+         *                           mem_cgroup_lookup()
+         *                           css_tryget()
+         *                           rcu_read_unlock()
+         * disable css_tryget()
+         * call_rcu()
+         *   offline_css()
+         *     reparent_charges()
+         *                           res_counter_charge()
+         *                           css_put()
+         *                             css_free()
+         *                           pc->mem_cgroup = dead memcg
+         *                           add page to lru
+         *
+         * The bulk of the charges are still moved in offline_css() to
+         * avoid pinning a lot of pages in case a long-term reference
+         * like a swapout record is deferring the css_free() to long
+         * after offlining.  But this makes sure we catch any charges
+         * made after offlining:
+         */
+        mem_cgroup_reparent_charges(memcg);
 
         memcg_destroy_kmem(memcg);
         __mem_cgroup_free(memcg);