netdev - [PATCH net-next] tcp: adopt try_cmpxchg() in tcp_release

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Message-ID: <20221110174829.3403442-1-edumazet@google.com>
Date:   Thu, 10 Nov 2022 17:48:29 +0000
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next] 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@...gle.com>
---
 net/ipv4/tcp_output.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c69f4d966024ce2c37dae63f7be94fe79c7dd648..d1cb1ecf8f216dc810ca08ea35ae752fd19ba706 100644
--- a/net/ipv4/tcp_output.c
+++ b/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);
-- 
2.38.1.431.g37b22c650d-goog