tcp: adopt try_cmpxchg() in tcp_release_cb()

try_cmpxchg() is slighly more efficient (at least on x86),
and smp_load_acquire(&sk->sk_tsq_flags) could avoid a KCSAN report.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20221110174829.3403442-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: edumazet

net/ipv4/tcp_output.c

@@ -1077,15 +1077,15 @@ static void tcp_tasklet_func(struct tasklet_struct *t)
  */
 void tcp_release_cb(struct sock *sk)
 {
-	unsigned long flags, nflags;
+	unsigned long flags = smp_load_acquire(&sk->sk_tsq_flags);
+	unsigned long nflags;
 
 	/* perform an atomic operation only if at least one flag is set */
 	do {
-		flags = sk->sk_tsq_flags;
 		if (!(flags & TCP_DEFERRED_ALL))
 			return;
 		nflags = flags & ~TCP_DEFERRED_ALL;
-	} while (cmpxchg(&sk->sk_tsq_flags, flags, nflags) != flags);
+	} while (!try_cmpxchg(&sk->sk_tsq_flags, &flags, nflags));
 
 	if (flags & TCPF_TSQ_DEFERRED) {
 		tcp_tsq_write(sk);