rxrpc: Use ACCESS_ONCE() when accessing circular buffer pointers

Use ACCESS_ONCE() when accessing the other-end pointer into a circular
buffer as it's possible the other-end pointer might change whilst we're
doing this, and if we access it twice, we might get some weird things
happening.

Signed-off-by: David Howells <dhowells@redhat.com>

diff --git a/net/rxrpc/ar-output.c b/net/rxrpc/ar-output.c
index 353f5c9..14c8df6 100644 (file)
--- a/net/rxrpc/ar-output.c
+++ b/net/rxrpc/ar-output.c
@@ -401,7 +401,8 @@ static int rxrpc_wait_for_tx_window(struct rxrpc_sock *rx,
        int ret;
 
        _enter(",{%d},%ld",
-              CIRC_SPACE(call->acks_head, call->acks_tail, call->acks_winsz),
+              CIRC_SPACE(call->acks_head, ACCESS_ONCE(call->acks_tail),
+                         call->acks_winsz),
               *timeo);
 
        add_wait_queue(&call->tx_waitq, &myself);
@@ -409,7 +410,7 @@ static int rxrpc_wait_for_tx_window(struct rxrpc_sock *rx,
        for (;;) {
                set_current_state(TASK_INTERRUPTIBLE);
                ret = 0;
-               if (CIRC_SPACE(call->acks_head, call->acks_tail,
+               if (CIRC_SPACE(call->acks_head, ACCESS_ONCE(call->acks_tail),
                               call->acks_winsz) > 0)
                        break;
                if (signal_pending(current)) {
@@ -570,7 +571,8 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
 
                        _debug("alloc");
 
-                       if (CIRC_SPACE(call->acks_head, call->acks_tail,
+                       if (CIRC_SPACE(call->acks_head,
+                                      ACCESS_ONCE(call->acks_tail),
                                       call->acks_winsz) <= 0) {
                                ret = -EAGAIN;
                                if (msg->msg_flags & MSG_DONTWAIT)
@@ -686,7 +688,8 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
                        sp->hdr.flags = conn->out_clientflag;
                        if (msg_data_left(msg) == 0 && !more)
                                sp->hdr.flags |= RXRPC_LAST_PACKET;
-                       else if (CIRC_SPACE(call->acks_head, call->acks_tail,
+                       else if (CIRC_SPACE(call->acks_head,
+                                           ACCESS_ONCE(call->acks_tail),
                                            call->acks_winsz) > 1)
                                sp->hdr.flags |= RXRPC_MORE_PACKETS;
                        if (more && seq & 1)