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From:   Muchun Song <songmuchun@bytedance.com>
To:     willy@infradead.org, akpm@linux-foundation.org, hannes@cmpxchg.org,
        mhocko@kernel.org, vdavydov.dev@gmail.com, shakeelb@google.com,
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Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-nfs@vger.kernel.org,
        zhengqi.arch@bytedance.com, duanxiongchun@bytedance.com,
        fam.zheng@bytedance.com, smuchun@gmail.com,
        Muchun Song <songmuchun@bytedance.com>
Subject: [PATCH v3 05/76] mm: list_lru: remove holding lru lock
Date:   Tue, 14 Sep 2021 15:28:27 +0800
Message-Id: <20210914072938.6440-6-songmuchun@bytedance.com>
In-Reply-To: <20210914072938.6440-1-songmuchun@bytedance.com>
References: <20210914072938.6440-1-songmuchun@bytedance.com>
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Since commit e5bc3af7734f ("rcu: Consolidate PREEMPT and !PREEMPT
synchronize_rcu()"), the critical section of spin lock can serve
as an RCU read-side critical section which already allows readers
that hold nlru->lock avoid taking rcu lock. So just to remove
holding lock.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/list_lru.c | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 4962d48d4410..6b2f3cbe5f67 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -402,18 +402,7 @@ static int memcg_update_list_lru_node(struct list_lru_node *nlru,
 	}
 
 	memcpy(&new->lru, &old->lru, old_size * sizeof(void *));
-
-	/*
-	 * The locking below allows readers that hold nlru->lock avoid taking
-	 * rcu_read_lock (see list_lru_from_memcg_idx).
-	 *
-	 * Since list_lru_{add,del} may be called under an IRQ-safe lock,
-	 * we have to use IRQ-safe primitives here to avoid deadlock.
-	 */
-	spin_lock_irq(&nlru->lock);
 	rcu_assign_pointer(nlru->memcg_lrus, new);
-	spin_unlock_irq(&nlru->lock);
-
 	kvfree_rcu(old, rcu);
 	return 0;
 }
-- 
2.11.0