net: sk_msg: Simplify sk_psock initialization

Initializing psock->sk_proto and other saved callbacks is only
done in sk_psock_update_proto, after sk_psock_init has returned.
The logic for this is difficult to follow, and needlessly complex.

Instead, initialize psock->sk_proto whenever we allocate a new
psock. Additionally, assert the following invariants:

* The SK has no ULP: ULP does it's own finagling of sk->sk_prot
* sk_user_data is unused: we need it to store sk_psock

Protect our access to sk_user_data with sk_callback_lock, which
is what other users like reuseport arrays, etc. do.

The result is that an sk_psock is always fully initialized, and
that psock->sk_proto is always the "original" struct proto.
The latter allows us to use psock->sk_proto when initializing
IPv6 TCP / UDP callbacks for sockmap.

Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200821102948.21918-2-lmb@cloudflare.com

1 files changed, 0 insertions, 17 deletions

diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index 1e9ed840b9fc..3119928fc103 100644
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -340,23 +340,6 @@ static inline void sk_psock_update_proto(struct sock *sk,
 					 struct sk_psock *psock,
 					 struct proto *ops)
 {
-	/* Initialize saved callbacks and original proto only once, since this
-	 * function may be called multiple times for a psock, e.g. when
-	 * psock->progs.msg_parser is updated.
-	 *
-	 * Since we've not installed the new proto, psock is not yet in use and
-	 * we can initialize it without synchronization.
-	 */
-	if (!psock->sk_proto) {
-		struct proto *orig = READ_ONCE(sk->sk_prot);
-
-		psock->saved_unhash = orig->unhash;
-		psock->saved_close = orig->close;
-		psock->saved_write_space = sk->sk_write_space;
-
-		psock->sk_proto = orig;
-	}
-
 	/* Pairs with lockless read in sk_clone_lock() */
 	WRITE_ONCE(sk->sk_prot, ops);
 }