[PATCH v6 5/8] netfilter: ipset: Don't use test_bit() in lockless RCU readers

[Jozsef Kadlecsik <kadlec@netfilter.org>]

Sashiko pointed out that there are a few lockless RCU readers
using test_bit() which is a relaxed atomic operation and
provides no memory barrier guarantees. Use test_bit_acquire()
instead where the operation may run parallel with add/del/gc,
i.e. is not one from the next cases

- protected by region lock
- in a set destroy phase
- in a new/temporary set creation phase

Also, add two missing smp_mb__after_atomic() operations.

Signed-off-by: Jozsef Kadlecsik <kadlec@netfilter.org>
---
 net/netfilter/ipset/ip_set_hash_gen.h | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/netfilter/ipset/ip_set_hash_gen.h b/net/netfilter/ipset/ip_set_hash_gen.h
index 04e4627ddfc1..6a31f2db824a 100644
--- a/net/netfilter/ipset/ip_set_hash_gen.h
+++ b/net/netfilter/ipset/ip_set_hash_gen.h
@@ -689,7 +689,7 @@ mtype_resize(struct ip_set *set, bool retried)
 				continue;
 			pos = smp_load_acquire(&n->pos);
 			for (j = 0; j < pos; j++) {
-				if (!test_bit(j, n->used))
+				if (!test_bit_acquire(j, n->used))
 					continue;
 				data = ahash_data(n, j, dsize);
 				if (SET_ELEM_EXPIRED(set, data))
@@ -826,7 +826,7 @@ mtype_ext_size(struct ip_set *set, u32 *elements, size_t *ext_size)
 				continue;
 			pos = smp_load_acquire(&n->pos);
 			for (j = 0; j < pos; j++) {
-				if (!test_bit(j, n->used))
+				if (!test_bit_acquire(j, n->used))
 					continue;
 				data = ahash_data(n, j, set->dsize);
 				if (!SET_ELEM_EXPIRED(set, data))
@@ -995,6 +995,7 @@ mtype_add(struct ip_set *set, void *value, const struct ip_set_ext *ext,
 	/* Ensure all data writes are visible before updating position */
 	smp_store_release(&n->pos, npos);
 	set_bit(j, n->used);
+	smp_mb__after_atomic();
 	if (old != ERR_PTR(-ENOENT)) {
 		rcu_assign_pointer(hbucket(t, key), n);
 		if (old)
@@ -1201,7 +1202,7 @@ mtype_test_cidrs(struct ip_set *set, struct mtype_elem *d,
 			continue;
 		pos = smp_load_acquire(&n->pos);
 		for (i = 0; i < pos; i++) {
-			if (!test_bit(i, n->used))
+			if (!test_bit_acquire(i, n->used))
 				continue;
 			data = ahash_data(n, i, set->dsize);
 			if (!mtype_data_equal(data, d, &multi))
@@ -1259,7 +1260,7 @@ mtype_test(struct ip_set *set, void *value, const struct ip_set_ext *ext,
 	}
 	pos = smp_load_acquire(&n->pos);
 	for (i = 0; i < pos; i++) {
-		if (!test_bit(i, n->used))
+		if (!test_bit_acquire(i, n->used))
 			continue;
 		data = ahash_data(n, i, set->dsize);
 		if (!mtype_data_equal(data, d, &multi))
@@ -1396,7 +1397,7 @@ mtype_list(const struct ip_set *set,
 			continue;
 		pos = smp_load_acquire(&n->pos);
 		for (i = 0; i < pos; i++) {
-			if (!test_bit(i, n->used))
+			if (!test_bit_acquire(i, n->used))
 				continue;
 			e = ahash_data(n, i, set->dsize);
 			if (SET_ELEM_EXPIRED(set, e))
-- 
2.39.5