Re: [PATCH bpf v3 2/2] bpf, sockmap: sk_prot needs inuse_idx set for proc stats

Jakub Sitnicki wrote:

On Tue, Jul 06, 2021 at 06:31 PM CEST, John Fastabend wrote:

quoted

Proc socket stats use sk_prot->inuse_idx value to record inuse sock stats.
We currently do not set this correctly from sockmap side. The result is
reading sock stats '/proc/net/sockstat' gives incorrect values. The
socket counter is incremented correctly, but because we don't set the
counter correctly when we replace sk_prot we may omit the decrement.

Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
 net/core/sock_map.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 60decd6420ca..27bdf768aa8c 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c

@@ -185,10 +185,19 @@ static void sock_map_unref(struct sock *sk, void *link_raw)

 static int sock_map_init_proto(struct sock *sk, struct sk_psock *psock)
 {
+	int err;
+#ifdef CONFIG_PROC_FS
+	int idx = sk->sk_prot->inuse_idx;
+#endif
 	if (!sk->sk_prot->psock_update_sk_prot)
 		return -EINVAL;
 	psock->psock_update_sk_prot = sk->sk_prot->psock_update_sk_prot;
-	return sk->sk_prot->psock_update_sk_prot(sk, psock, false);
+	err = sk->sk_prot->psock_update_sk_prot(sk, psock, false);
+#ifdef CONFIG_PROC_FS
+	if (!err)
+		sk->sk_prot->inuse_idx = idx;
+#endif
+	return err;
 }

 static struct sk_psock *sock_map_psock_get_checked(struct sock *sk)

We could initialize inuse_idx just once in {tcp,udp}_bpf_rebuild_protos,
if we changed {tcp,udp}_bpf_v4_build_proto to be a late_initcall, so
that it runs after inet_init when {tcp,udp}_prot and udp_prot are
already registered and have inuse_idx assigned.

OK does seem slightly nicer. Then I guess the diff is just,

diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index f26916a62f25..d3e9386b493e 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c

@@ -503,7 +503,7 @@ static int __init tcp_bpf_v4_build_proto(void)
        tcp_bpf_rebuild_protos(tcp_bpf_prots[TCP_BPF_IPV4], &tcp_prot);
        return 0;
 }
-core_initcall(tcp_bpf_v4_build_proto);
+late_initcall(tcp_bpf_v4_build_proto);
 
 static int tcp_bpf_assert_proto_ops(struct proto *ops)
 {