1 files changed, 18 insertions, 0 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0f1f7a7374ba..36896f3eb7f5 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -250,6 +250,14 @@ static struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
 
 struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
 {
+        /*
+         * mm_update_next_owner() may clear mm->owner to NULL
+         * if it races with swapoff, page migration, etc.
+         * So this can be called with p == NULL.
+         */
+        if (unlikely(!p))
+                return NULL;
+
         return container_of(task_subsys_state(p, mem_cgroup_subsys_id),
                                 struct mem_cgroup, css);
 }
@@ -549,6 +557,11 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
         if (likely(!memcg)) {
                 rcu_read_lock();
                 mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
+                if (unlikely(!mem)) {
+                        rcu_read_unlock();
+                        kmem_cache_free(page_cgroup_cache, pc);
+                        return 0;
+                }
                 /*
                  * For every charge from the cgroup, increment reference count
                  */
@@ -801,11 +814,16 @@ int mem_cgroup_shrink_usage(struct mm_struct *mm, gfp_t gfp_mask)
 
         rcu_read_lock();
         mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
+        if (unlikely(!mem)) {
+                rcu_read_unlock();
+                return 0;
+        }
         css_get(&mem->css);
         rcu_read_unlock();
 
         do {
                 progress = try_to_free_mem_cgroup_pages(mem, gfp_mask);
+                progress += res_counter_check_under_limit(&mem->res);
         } while (!progress && --retry);
 
         css_put(&mem->css);