rxrpc: Don't need barrier for ->tx_bottom and ->acks_hard_ack

We don't need a barrier for the ->tx_bottom value (which indicates the
lowest sequence still in the transmission queue) and the ->acks_hard_ack
value (which tracks the DATA packets hard-ack'd by the latest ACK packet
received and thus indicates which DATA packets can now be discarded) as the
app thread doesn't use either value as a reference to memory to access.
Rather, the app thread merely uses these as a guide to how much space is
available in the transmission queue

Change the code to use READ/WRITE_ONCE() instead.

Also, change rxrpc_check_tx_space() to use the same value for tx_bottom
throughout.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://patch.msgid.link/20241204074710.990092-18-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
index 786c1fb1369abe789114fb525035308c10f6274c..467c9402882e67fe0188468bef107ce83501cf21 100644 (file)
--- a/net/rxrpc/sendmsg.c
+++ b/net/rxrpc/sendmsg.c
@@ -94,9 +94,11 @@ no_wait:
  */
 static bool rxrpc_check_tx_space(struct rxrpc_call *call, rxrpc_seq_t *_tx_win)
 {
+       rxrpc_seq_t tx_bottom = READ_ONCE(call->tx_bottom);
+
        if (_tx_win)
-               *_tx_win = call->tx_bottom;
-       return call->tx_prepared - call->tx_bottom < 256;
+               *_tx_win = tx_bottom;
+       return call->tx_prepared - tx_bottom < 256;
 }
 
 /*
@@ -138,7 +140,7 @@ static int rxrpc_wait_for_tx_window_waitall(struct rxrpc_sock *rx,
                rtt = 2;
 
        timeout = rtt;
-       tx_start = smp_load_acquire(&call->acks_hard_ack);
+       tx_start = READ_ONCE(call->acks_hard_ack);
 
        for (;;) {
                set_current_state(TASK_UNINTERRUPTIBLE);

diff --git a/net/rxrpc/txbuf.c b/net/rxrpc/txbuf.c
index 8b7c854ed3d7581bf7a39c3cbb398cc5194da900..0cc8f49d69a9e455d7cdbeb0fd8932e8fbe0878e 100644 (file)
--- a/net/rxrpc/txbuf.c
+++ b/net/rxrpc/txbuf.c
@@ -214,14 +214,14 @@ void rxrpc_shrink_call_tx_buffer(struct rxrpc_call *call)
 
        while ((txb = list_first_entry_or_null(&call->tx_buffer,
                                               struct rxrpc_txbuf, call_link))) {
-               hard_ack = smp_load_acquire(&call->acks_hard_ack);
+               hard_ack = call->acks_hard_ack;
                if (before(hard_ack, txb->seq))
                        break;
 
                if (txb->seq != call->tx_bottom + 1)
                        rxrpc_see_txbuf(txb, rxrpc_txbuf_see_out_of_step);
                ASSERTCMP(txb->seq, ==, call->tx_bottom + 1);
-               smp_store_release(&call->tx_bottom, call->tx_bottom + 1);
+               WRITE_ONCE(call->tx_bottom, call->tx_bottom + 1);
                list_del_rcu(&txb->call_link);
 
                trace_rxrpc_txqueue(call, rxrpc_txqueue_dequeue);