 @@ -1,41 +1,41 @@
-/*      $NetBSD: xennetback_xenbus.c,v 1.118 2023/08/09 08:38:05 riastradh Exp $      */
+/*      $NetBSD: xennetback_xenbus.c,v 1.119 2023/08/09 08:38:16 riastradh Exp $      */
 /*
  * Copyright (c) 2006 Manuel Bouyer.
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
+ *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: xennetback_xenbus.c,v 1.118 2023/08/09 08:38:05 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: xennetback_xenbus.c,v 1.119 2023/08/09 08:38:16 riastradh Exp $");
 #include <sys/types.h>
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/kmem.h>
 #include <sys/queue.h>
 #include <sys/kernel.h>
 #include <sys/mbuf.h>
 #include <sys/protosw.h>
 #include <sys/socket.h>
 #include <sys/ioctl.h>
 #include <sys/errno.h>
 #include <sys/device.h>
 @@ -801,44 +801,36 @@ static int
 xennetback_evthandler(void *arg)
+{
 	struct xnetback_instance *xneti = arg;
 	struct ifnet *ifp = &xneti->xni_if;
 	netif_tx_request_t txreq;
 	struct mbuf *m, *m0 = NULL, *mlast = NULL;
 	int receive_pending;
 	int queued = 0, m0_len = 0;
 	struct xnetback_xstate *xst;
 	const bool discard = ((ifp->if_flags & (IFF_UP | IFF_RUNNING)) !=
 	    (IFF_UP | IFF_RUNNING));
 	XENPRINTF(("xennetback_evthandler "));
 again:
 	while (1) {
 		/*
 		 * XXX The xen_rmb here and comment make no sense:
 		 * xneti->xni_txring.req_cons is a private variable.
 		 */
 		xen_rmb(); /* be sure to read the request before updating */
 		/* XXX Unclear what this xen_wmb is for.  */
 		xen_wmb();
-		/*
+		if (!RING_HAS_UNCONSUMED_REQUESTS(&xneti->xni_txring))
 		 * XXX RING_FINAL_CHECK_FOR_REQUESTS issues the most
 		 * expensive memory barrier, xen_mb.  This should be
 		 * used only at the end of the loop after we updating
 		 * the producer with the last index of the requests we
 		 * consumed in the queue.
 		 */
 		RING_FINAL_CHECK_FOR_REQUESTS(&xneti->xni_txring,
 		    receive_pending);
 		if (receive_pending == 0)
 			break;
 		/*
 		 * Ensure we have read the producer's queue index in
 		 * RING_FINAL_CHECK_FOR_REQUESTS before we read the
 		 * content of the producer's next request in
 		 * RING_COPY_REQUEST.
 		 */
 		xen_rmb();
 		RING_COPY_REQUEST(&xneti->xni_txring,
 		    xneti->xni_txring.req_cons,
 		    &txreq);
 		/* XXX Unclear what this xen_rmb is for. */
 		xen_rmb();
 @@ -971,26 +963,29 @@ mbuf_fail:
 		KASSERT(queued <= NB_XMIT_PAGES_BATCH);
 		if (__predict_false(m0 &&
 		    (txreq.flags & NETTXF_more_data) == 0)) {
 			/* Last fragment, stop appending mbufs */
 			m0 = NULL;
+		}
 		if (queued == NB_XMIT_PAGES_BATCH) {
 			KASSERT(m0 == NULL);
 			xennetback_tx_copy_process(ifp, xneti, queued);
 			queued = 0;
+		}
+	}
 	RING_FINAL_CHECK_FOR_REQUESTS(&xneti->xni_txring, receive_pending);
 	if (receive_pending)
 		goto again;
 	if (m0) {
 		/* Queue empty, and still unfinished multi-fragment request */
 		printf("%s: dropped unfinished multi-fragment\n",
 		    ifp->if_xname);
 		xennetback_tx_copy_abort(ifp, xneti, queued);
 		queued = 0;
 		m0 = NULL;
+	}
 	if (queued > 0)
 		xennetback_tx_copy_process(ifp, xneti, queued);
 	/* check to see if we can transmit more packets */
 	if_schedule_deferred_start(ifp);