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Subject[tip: core/rcu] kvfree_rcu: Use [READ/WRITE]_ONCE() macros to access to nr_bkv_objs
The following commit has been merged into the core/rcu branch of tip:

Commit-ID: ac7625ebd5f7bad93f821b7397fe50635f58aa4b
Gitweb: https://git.kernel.org/tip/ac7625ebd5f7bad93f821b7397fe50635f58aa4b
Author: Uladzislau Rezki (Sony) <urezki@gmail.com>
AuthorDate: Thu, 15 Apr 2021 19:19:57 +02:00
Committer: Paul E. McKenney <paulmck@kernel.org>
CommitterDate: Mon, 10 May 2021 16:00:48 -07:00

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>
---
kernel/rcu/tree.c | 14 ++++----------
1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 74d840a..676a49a 100644
--- 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);
}

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