tcp: no longer release socket ownership in tcp_release_cb()

This partially reverts c3f9b018 ("tcp: tcp_release_cb()
should release socket ownership").

prequeue has been removed by Florian in commit e7942d06
("tcp: remove prequeue support")

__tcp_checksum_complete_user() being gone, we no longer
have to release socket ownership in tcp_release_cb().

This is a prereq for third patch in the series
("net: call prot->release_cb() when processing backlog").
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/core/sock.c

@@ -3519,9 +3519,6 @@ void release_sock(struct sock *sk)
 	if (sk->sk_backlog.tail)
 		__release_sock(sk);
 
-	/* Warning : release_cb() might need to release sk ownership,
-	 * ie call sock_release_ownership(sk) before us.
-	 */
 	if (sk->sk_prot->release_cb)
 		sk->sk_prot->release_cb(sk);
 

net/ipv4/tcp_output.c

@@ -1101,16 +1101,6 @@ void tcp_release_cb(struct sock *sk)
 		tcp_tsq_write(sk);
 		__sock_put(sk);
 	}
-	/* Here begins the tricky part :
-	 * We are called from release_sock() with :
-	 * 1) BH disabled
-	 * 2) sk_lock.slock spinlock held
-	 * 3) socket owned by us (sk->sk_lock.owned == 1)
-	 *
-	 * But following code is meant to be called from BH handlers,
-	 * so we should keep BH disabled, but early release socket ownership
-	 */
-	sock_release_ownership(sk);
 
 	if (flags & TCPF_WRITE_TIMER_DEFERRED) {
 		tcp_write_timer_handler(sk);