Re: [PATCH] mm: memcontrol: fix get_active_memcg return value

On Tue, Feb 23, 2021 at 1:14 AM Muchun Song songmuchun@bytedance.com wrote:

We use a global percpu int_active_memcg variable to store the remote memcg when we are in the interrupt context. But get_active_memcg always return the current->active_memcg or root_mem_cgroup. The remote memcg (set in the interrupt context) is ignored. This is not what we want. So fix it.

Fixes: 37d5985c003d ("mm: kmem: prepare remote memcg charging infra for interrupt contexts") Signed-off-by: Muchun Song songmuchun@bytedance.com

Good catch. Cc: stable@vger.kernel.org

Reviewed-by: Shakeel Butt shakeelb@google.com

---

mm/memcontrol.c | 10 +++------- 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c index be6bc5044150..bbe25655f7eb 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1061,13 +1061,9 @@ static __always_inline struct mem_cgroup *get_active_memcg(void)

    rcu_read_lock();
    memcg = active_memcg();

•   if (memcg) {
  

•           /* current->active_memcg must hold a ref. */
  

•           if (WARN_ON_ONCE(!css_tryget(&memcg->css)))
  

•                   memcg = root_mem_cgroup;
  

•           else
  

•                   memcg = current->active_memcg;
  

•   }
  

•   /* remote memcg must hold a ref. */
  

•   if (memcg && WARN_ON_ONCE(!css_tryget(&memcg->css)))
  

•           memcg = root_mem_cgroup;
    rcu_read_unlock();
  
    return memcg;
  

-- 2.11.0