mm: memcontrol: make all the callers of {folio,page}_memcg() safe

mm: memcontrol: make all the callers of {folio,page}_memcg() safe

When we use objcg APIs to charge the LRU pages, the page will not hold a
reference to the memcg associated with the page.  So the caller of the
{folio,page}_memcg() should hold an rcu read lock or obtain a reference to
the memcg associated with the page to protect memcg from being released.
So introduce get_mem_cgroup_from_{page,folio}() to obtain a reference to
the memory cgroup associated with the page.

In this patch, make all the callers hold an rcu read lock or obtain a
reference to the memcg to protect memcg from being released when the LRU
pages reparented.

We do not need to adjust the callers of {folio,page}_memcg() during the
whole process of mem_cgroup_move_task().  Because the cgroup migration and
memory cgroup offlining are serialized by @cgroup_mutex.  In this routine,
the LRU pages cannot be reparented to its parent memory cgroup.  So
{folio,page}_memcg() is stable and cannot be released.

This is a preparation for reparenting the LRU pages.

Link: https://lkml.kernel.org/r/20220621125658.64935-8-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>