[PATCH v1 01/14] include/linux/memcontrol.h: do not warn in page_memcg_rcu() if !CONFIG_MEMCG

[Yu Zhao]

We want to make sure the rcu lock is held while using
page_memcg_rcu(). But having a WARN_ON_ONCE() in page_memcg_rcu() when
!CONFIG_MEMCG is superfluous because of the following legit use case:

  memcg = lock_page_memcg(page1)
    (rcu_read_lock() if CONFIG_MEMCG=y)

  do something to page1

  if (page_memcg_rcu(page2) == memcg)
    do something to page2 too as it cannot be migrated away from the
    memcg either.

  unlock_page_memcg(page1)
    (rcu_read_unlock() if CONFIG_MEMCG=y)

This patch removes the WARN_ON_ONCE() from page_memcg_rcu() for the
!CONFIG_MEMCG case.

Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
---
 include/linux/memcontrol.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index e6dc793d587d..f325aeb4b4e8 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1079,7 +1079,6 @@ static inline struct mem_cgroup *page_memcg(struct page *page)
 
 static inline struct mem_cgroup *page_memcg_rcu(struct page *page)
 {
-	WARN_ON_ONCE(!rcu_read_lock_held());
 	return NULL;
 }
 
-- 
2.31.0.rc2.261.g7f71774620-goog