mm: list_lru: remove holding lru lock

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 to avoid taking rcu lock.  So just remove holding lock.

Link: https://lkml.kernel.org/r/20211025124534.56345-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/list_lru.c b/mm/list_lru.c
index a6031f1..9a1f7df 100644 (file)
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -398,18 +398,7 @@ static int memcg_update_list_lru_node(struct list_lru_node *nlru,
        }
 
        memcpy(&new->lru, &old->lru, flex_array_size(new, lru, old_size));
-
-       /*
-        * 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;
 }