mm: kmem: remove redundant checks from get_obj_cgroup_from_current()

There are checks for current->mm and current->active_memcg in
get_obj_cgroup_from_current(), but these checks are redundant:
memcg_kmem_bypass() called just above performs same checks.

Signed-off-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Link: http://lkml.kernel.org/r/20200827225843.1270629-3-guro@fb.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -2939,9 +2939,6 @@ __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void)
 	if (memcg_kmem_bypass())
 		return NULL;
 
-	if (unlikely(!current->mm && !current->active_memcg))
-		return NULL;
-
 	rcu_read_lock();
 	if (unlikely(current->active_memcg))
 		memcg = rcu_dereference(current->active_memcg);