kvfree_rcu: Use [READ/WRITE]_ONCE() macros to access to nr_bkv_objs

nr_bkv_objs is a count of the objects in the kvfree_rcu page cache.
Accessing it requires holding the ->lock.  Switch to READ_ONCE() and
WRITE_ONCE() macros to provide lockless access to this counter.
This lockless access is used for the shrinker.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 74d840aa877bec5d512a009cd8afdcf098e150e1..676a49ab5b2b482019150bd9581c951ac2046f0b 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3250,7 +3250,7 @@ get_cached_bnode(struct kfree_rcu_cpu *krcp)
        if (!krcp->nr_bkv_objs)
                return NULL;
 
-       krcp->nr_bkv_objs--;
+       WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs - 1);
        return (struct kvfree_rcu_bulk_data *)
                llist_del_first(&krcp->bkvcache);
 }
@@ -3264,9 +3264,8 @@ put_cached_bnode(struct kfree_rcu_cpu *krcp,
                return false;
 
        llist_add((struct llist_node *) bnode, &krcp->bkvcache);
-       krcp->nr_bkv_objs++;
+       WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs + 1);
        return true;
-
 }
 
 static int
@@ -3278,7 +3277,7 @@ drain_page_cache(struct kfree_rcu_cpu *krcp)
 
        raw_spin_lock_irqsave(&krcp->lock, flags);
        page_list = llist_del_all(&krcp->bkvcache);
-       krcp->nr_bkv_objs = 0;
+       WRITE_ONCE(krcp->nr_bkv_objs, 0);
        raw_spin_unlock_irqrestore(&krcp->lock, flags);
 
        llist_for_each_safe(pos, n, page_list) {
@@ -3682,18 +3681,13 @@ kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
 {
        int cpu;
        unsigned long count = 0;
-       unsigned long flags;
 
        /* Snapshot count of all CPUs */
        for_each_possible_cpu(cpu) {
                struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
 
                count += READ_ONCE(krcp->count);
-
-               raw_spin_lock_irqsave(&krcp->lock, flags);
-               count += krcp->nr_bkv_objs;
-               raw_spin_unlock_irqrestore(&krcp->lock, flags);
-
+               count += READ_ONCE(krcp->nr_bkv_objs);
                atomic_set(&krcp->backoff_page_cache_fill, 1);
        }