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

David Howells
2024-03-06T00:07:18Z

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@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.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 */