page_memcg_rcu() warns on !rcu_read_lock_held() regardless of
CONFIG_MEMCG. The following legit code trips the warning when
!CONFIG_MEMCG, since lock_page_memcg() and unlock_page_memcg() are
empty for this config.
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)
Locking/unlocking rcu consistently for both configs is rigorous but it
also forces unnecessary locking upon users who have no interest in
CONFIG_MEMCG.
This patch removes the assertion for !CONFIG_MEMCG, because
page_memcg_rcu() has a few callers and there are no concerns regarding
their correctness at the moment.
Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Tested-by: Konstantin Kharlamov <Hi-Angel@xxxxxxxxx>
---
include/linux/memcontrol.h | 1 -
1 file changed, 1 deletion(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index c193be760709..6bcac3d91dd1 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1131,7 +1131,6 @@ 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;
}
--
2.31.1.751.gd2f1c929bd-goog
