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charset="UTF-8" Precedence: bulk List-ID: <linux-kernel.vger.kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Archive: <https://lore.kernel.org/lkml/> 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@google.com> Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru> --- 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