netdev - [PATCH net-next v3 06/21] rxrpc: Remove atomic handling on some fields only used in I/O thread

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Date: Wed,  6 Mar 2024 00:06:36 +0000
From: David Howells <dhowells@...hat.com>
To: netdev@...r.kernel.org
Cc: David Howells <dhowells@...hat.com>,
	Marc Dionne <marc.dionne@...istor.com>,
	Simon Horman <horms@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	linux-afs@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH net-next v3 06/21] rxrpc: Remove atomic handling on some fields only used in I/O thread

call->tx_transmitted and call->acks_prev_seq don't need to be managed with
cmpxchg() and barriers as it's only used within the singular I/O thread.

Signed-off-by: David Howells <dhowells@...hat.com>
cc: Marc Dionne <marc.dionne@...istor.com>
cc: "David S. Miller" <davem@...emloft.net>
cc: Eric Dumazet <edumazet@...gle.com>
cc: Jakub Kicinski <kuba@...nel.org>
cc: Paolo Abeni <pabeni@...hat.com>
cc: linux-afs@...ts.infradead.org
cc: netdev@...r.kernel.org
---
 net/rxrpc/call_event.c | 10 ++++------
 net/rxrpc/output.c     |  8 +++-----
 2 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/net/rxrpc/call_event.c b/net/rxrpc/call_event.c
index 84eedbb49fcb..1184518dcdb8 100644
--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c
@@ -115,7 +115,7 @@ void rxrpc_resend(struct rxrpc_call *call, struct sk_buff *ack_skb)
 	struct rxrpc_skb_priv *sp;
 	struct rxrpc_txbuf *txb;
 	unsigned long resend_at;
-	rxrpc_seq_t transmitted = READ_ONCE(call->tx_transmitted);
+	rxrpc_seq_t transmitted = call->tx_transmitted;
 	ktime_t now, max_age, oldest, ack_ts;
 	bool unacked = false;
 	unsigned int i;
@@ -184,16 +184,14 @@ void rxrpc_resend(struct rxrpc_call *call, struct sk_buff *ack_skb)
 	 * seen.  Anything between the soft-ACK table and that point will get
 	 * ACK'd or NACK'd in due course, so don't worry about it here; here we
 	 * need to consider retransmitting anything beyond that point.
-	 *
-	 * Note that ACK for a packet can beat the update of tx_transmitted.
 	 */
-	if (after_eq(READ_ONCE(call->acks_prev_seq), READ_ONCE(call->tx_transmitted)))
+	if (after_eq(call->acks_prev_seq, call->tx_transmitted))
 		goto no_further_resend;
 
 	list_for_each_entry_from(txb, &call->tx_buffer, call_link) {
-		if (before_eq(txb->seq, READ_ONCE(call->acks_prev_seq)))
+		if (before_eq(txb->seq, call->acks_prev_seq))
 			continue;
-		if (after(txb->seq, READ_ONCE(call->tx_transmitted)))
+		if (after(txb->seq, call->tx_transmitted))
 			break; /* Not transmitted yet */
 
 		if (ack && ack->reason == RXRPC_ACK_PING_RESPONSE &&
diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index 2386b01b2231..1e039b6f4494 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -397,12 +397,10 @@ int rxrpc_send_data_packet(struct rxrpc_call *call, struct rxrpc_txbuf *txb)
 
 	/* Track what we've attempted to transmit at least once so that the
 	 * retransmission algorithm doesn't try to resend what we haven't sent
-	 * yet.  However, this can race as we can receive an ACK before we get
-	 * to this point.  But, OTOH, if we won't get an ACK mentioning this
-	 * packet unless the far side received it (though it could have
-	 * discarded it anyway and NAK'd it).
+	 * yet.
 	 */
-	cmpxchg(&call->tx_transmitted, txb->seq - 1, txb->seq);
+	if (txb->seq == call->tx_transmitted + 1)
+		call->tx_transmitted = txb->seq;
 
 	/* send the packet with the don't fragment bit set if we currently
 	 * think it's small enough */