[PATCH v2] memcg: Fix memcg_kmem_bypass() for remote memcg charging

Zefan Li
2020-05-13T11:47:49Z

While trying to use remote memcg charging in an out-of-tree kernel module
I found it's not working, because the current thread is a workqueue thread.

As we will probably encounter this issue in the future as the users of
memalloc_use_memcg() grow, it's better we fix it now.

Signed-off-by: Zefan Li <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
---

v2: add a comment as sugguested by Michal. and add changelog to explain why
upstream kernel needs this fix.

---

mm/memcontrol.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a3b97f1..43a12ed 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2802,6 +2802,9 @@ static void memcg_schedule_kmem_cache_create(struct mem_cgroup *memcg,

static inline bool memcg_kmem_bypass(void)
{
+ /* Allow remote memcg charging in kthread contexts. */
+ if (unlikely(current->active_memcg))
+ return false;
if (in_interrupt() || !current->mm || (current->flags & PF_KTHREAD))
return true;
return false;
--
2.7.4