[PATCH bpf-next v4 2/2] xsk: support BPF_EXIST and BPF_NOEXIST flags in XSKMAP

[Björn Töpel <bjorn.topel@xxxxxxxxx>]

From: Björn Töpel <bjorn.topel@xxxxxxxxx>

The XSKMAP did not honor the BPF_EXIST/BPF_NOEXIST flags when updating
an entry. This patch addresses that.

Signed-off-by: Björn Töpel <bjorn.topel@xxxxxxxxx>
---
 kernel/bpf/xskmap.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/xskmap.c b/kernel/bpf/xskmap.c
index 780639309f6b..8864dfe1d9ef 100644
--- a/kernel/bpf/xskmap.c
+++ b/kernel/bpf/xskmap.c
@@ -226,8 +226,6 @@ static int xsk_map_update_elem(struct bpf_map *map, void *key, void *value,
 		return -EINVAL;
 	if (unlikely(i >= m->map.max_entries))
 		return -E2BIG;
-	if (unlikely(map_flags == BPF_NOEXIST))
-		return -EEXIST;
 
 	sock = sockfd_lookup(fd, &err);
 	if (!sock)
@@ -253,14 +251,29 @@ static int xsk_map_update_elem(struct bpf_map *map, void *key, void *value,
 	}
 
 	spin_lock_bh(&m->lock);
+	entry = &m->xsk_map[i];
+	old_xs = READ_ONCE(*entry);
+	if (old_xs && map_flags == BPF_NOEXIST) {
+		err = -EEXIST;
+		goto out;
+	} else if (!old_xs && map_flags == BPF_EXIST) {
+		err = -ENOENT;
+		goto out;
+	}
 	xsk_map_sock_add(xs, node);
-	old_xs = xchg(entry, xs);
+	WRITE_ONCE(*entry, xs);
 	if (old_xs)
 		xsk_map_sock_delete(old_xs, entry);
 	spin_unlock_bh(&m->lock);
 
 	sockfd_put(sock);
 	return 0;
+
+out:
+	spin_unlock_bh(&m->lock);
+	sockfd_put(sock);
+	xsk_map_node_free(node);
+	return err;
 }
 
 static int xsk_map_delete_elem(struct bpf_map *map, void *key)
-- 
2.20.1