netdev - [PATCH net-next] net/tcp_fastopen: remove tcp_fastopen_ctx

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Date:   Mon, 19 Jul 2021 03:11:07 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Wei Wang <weiwan@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: [PATCH net-next] net/tcp_fastopen: remove tcp_fastopen_ctx_lock

From: Eric Dumazet <edumazet@...gle.com>

Remove the (per netns) spinlock in favor of xchg() atomic operations.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Wei Wang <weiwan@...gle.com>
Cc: Yuchung Cheng <ycheng@...gle.com>
Cc: Neal Cardwell <ncardwell@...gle.com>
---
 include/net/netns/ipv4.h |  1 -
 net/ipv4/tcp_fastopen.c  | 17 +++--------------
 net/ipv4/tcp_ipv4.c      |  1 -
 3 files changed, 3 insertions(+), 16 deletions(-)

diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index b8620519eace8191c76c41f37bd51ac0d3788bc2..2f65701a43c953bd3a9a9e3d491882cb7bb11859 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -174,7 +174,6 @@ struct netns_ipv4 {
 	int sysctl_tcp_fastopen;
 	const struct tcp_congestion_ops __rcu  *tcp_congestion_control;
 	struct tcp_fastopen_context __rcu *tcp_fastopen_ctx;
-	spinlock_t tcp_fastopen_ctx_lock;
 	unsigned int sysctl_tcp_fastopen_blackhole_timeout;
 	atomic_t tfo_active_disable_times;
 	unsigned long tfo_active_disable_stamp;
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 47c32604d38fca960d2cd56f3588bfd2e390b789..1a9fbd5448a719bb5407a8d1e8fbfbe54f56f258 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -55,12 +55,7 @@ void tcp_fastopen_ctx_destroy(struct net *net)
 {
 	struct tcp_fastopen_context *ctxt;
 
-	spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);
-
-	ctxt = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
-				lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
-	rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, NULL);
-	spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
+	ctxt = xchg((__force struct tcp_fastopen_context **)&net->ipv4.tcp_fastopen_ctx, NULL);
 
 	if (ctxt)
 		call_rcu(&ctxt->rcu, tcp_fastopen_ctx_free);
@@ -89,18 +84,12 @@ int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
 		ctx->num = 1;
 	}
 
-	spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);
 	if (sk) {
 		q = &inet_csk(sk)->icsk_accept_queue.fastopenq;
-		octx = rcu_dereference_protected(q->ctx,
-			lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
-		rcu_assign_pointer(q->ctx, ctx);
+		octx = xchg((__force struct tcp_fastopen_context **)&q->ctx, ctx);
 	} else {
-		octx = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
-			lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
-		rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, ctx);
+		octx = xchg((__force struct tcp_fastopen_context **)&net->ipv4.tcp_fastopen_ctx, ctx);
 	}
-	spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
 
 	if (octx)
 		call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index b9dc2d6197be8b8b03a4d052ad1c87987c7a62aa..e9321dd39cdbcb664843d4ada09a21685b93abb7 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2964,7 +2964,6 @@ static int __net_init tcp_sk_init(struct net *net)
 	net->ipv4.sysctl_tcp_comp_sack_slack_ns = 100 * NSEC_PER_USEC;
 	net->ipv4.sysctl_tcp_comp_sack_nr = 44;
 	net->ipv4.sysctl_tcp_fastopen = TFO_CLIENT_ENABLE;
-	spin_lock_init(&net->ipv4.tcp_fastopen_ctx_lock);
 	net->ipv4.sysctl_tcp_fastopen_blackhole_timeout = 60 * 60;
 	atomic_set(&net->ipv4.tfo_active_disable_times, 0);
 
-- 
2.32.0.402.g57bb445576-goog