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[v2,01/16] include/linux/memcontrol.h: do not warn in page_memcg_rcu() if !CONFIG_MEMCG

Message ID 20210413065633.2782273-2-yuzhao@google.com (mailing list archive)
State New
Headers show
Series Multigenerational LRU Framework | expand

Commit Message

Yu Zhao April 13, 2021, 6:56 a.m. UTC
page_memcg_rcu() warns on !rcu_read_lock_held() regardless of
CONFIG_MEMCG. The following code is legit, but it triggers 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.

    (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

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@google.com>
 include/linux/memcontrol.h | 1 -
 1 file changed, 1 deletion(-)
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diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 0c04d39a7967..f13dc02cf277 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1077,7 +1077,6 @@  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;