sys/net/gnrc/netif: hold packets after tx_sync split

sys/net/gnrc/netif/gnrc_netif.c

@@ -1922,11 +1922,6 @@
             /* try to send anyway */
         }
     }
-    /* hold in case device was busy to not having to rewrite *all* the link
-     * layer implementations in case `gnrc_netif_pktq` is included */
-    if (gnrc_netif_netdev_legacy_api(netif)) {
-        gnrc_pktbuf_hold(pkt, 1);
-    }
 #endif /* IS_USED(MODULE_GNRC_NETIF_PKTQ) */
 
     /* Record send in neighbor statistics if destination is unicast */
@@ -1947,6 +1942,13 @@
     /* Split off the TX sync snip */
     gnrc_pktsnip_t *tx_sync = IS_USED(MODULE_GNRC_TX_SYNC)
                             ? gnrc_tx_sync_split(pkt) : NULL;
+#if IS_USED(MODULE_GNRC_NETIF_PKTQ)
+    /* hold in case device was busy to not having to rewrite *all* the link
+     * layer implementations in case `gnrc_netif_pktq` is included */
+    if (gnrc_netif_netdev_legacy_api(netif)) {
+        gnrc_pktbuf_hold(pkt, 1);
+    }
+#endif /* IS_USED(MODULE_GNRC_NETIF_PKTQ) */
     int res = netif->ops->send(netif, pkt);
 
     /* For legacy netdevs (no confirm_send) TX is blocking, thus it is always
@@ -2195,4 +2197,4 @@
         }
     }
 }
 /** @} */

tests/net/gnrc_legacy_tx_sync/Makefile

@@ -0,0 +1,12 @@
+include ../Makefile.net_common
+
+USEMODULE += netdev_default
+USEMODULE += auto_init_gnrc_netif
+USEMODULE += gnrc_tx_sync
+USEMODULE += gnrc_netif_pktq
+USEMODULE += nrfmin
+USEMODULE += ztimer_sec
+
+include $(RIOTBASE)/Makefile.include
+
+CFLAGS += -DDEBUG_ASSERT_VERBOSE=1

tests/net/gnrc_legacy_tx_sync/main.c

@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2025 Technische Universität Dresden
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @{
+ *
+ * @file
+ * @brief       Text application for gnrc_legacy_tx_sync
+ *
+ * @author      Lukas Luger     <[email protected]>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+
+#include "net/af.h"
+#include "net/gnrc/pktbuf.h"
+#include "net/gnrc/tx_sync.h"
+#include "net/gnrc.h"
+#include "ztimer.h"
+#include "thread.h"
+
+static char result_thread_stack[THREAD_STACKSIZE_MAIN];
+
+static const char test_msg[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTU"
+                               "VWXYZ0123456789.,:;!?@#$%^&*()[]{}-_=+/<>`~\'\""
+                               "\\";
+
+void *result_thread(void *arg)
+{
+    (void)arg;
+    /* Only receiving one message ever */
+    msg_t msg;
+    msg_receive(&msg);
+    if (msg.content.value) {
+        puts("TEST PASSED");
+    }
+    else {
+        puts("TEST FAILED");
+    }
+    return NULL;
+}
+
+int main(void)
+{
+    puts(
+        "Test application for gnrc_legacy_tx_sync\n"
+        "========================================\n"
+        "\n"
+        "This application sends a single message over the nrfmin netdev.\n"
+        "Other legacy netdevs can be used by changing the board and using\n"
+        "a different driver. Note: RIOT will sometimes choose the\n"
+        "netdev_ieee802154_submac as default driver which is not legacy.\n"
+        "tx_sync will only fail if gnrc_netif_pktq is used with a legacy driver.\n"
+        "If tx_sync does not finish in one second, the test will fail.\n"
+    );
+
+    msg_t error_msg = { .content.value = 0 };
+    msg_t success_msg = { .content.value = 1 };
+
+    /* Preparing the gnrc message */
+    gnrc_netif_t *netif = gnrc_netif_iter(NULL);
+    gnrc_pktsnip_t *pkt = gnrc_pktbuf_add(NULL, test_msg, sizeof(test_msg),
+                                                        GNRC_NETTYPE_UNDEF);
+    gnrc_tx_sync_t tx_sync;
+    gnrc_tx_sync_append(pkt, &tx_sync);
+
+    /* Starting the result thread */
+    pid_t pid = thread_create(result_thread_stack, sizeof(result_thread_stack),
+                                THREAD_PRIORITY_MAIN - 1, 0, result_thread, NULL,
+                                "result_thread");
+
+    /* Set timeout message in case tx sync fails */
+    ztimer_t timer;
+    ztimer_set_msg(ZTIMER_SEC, &timer, 1, &error_msg, pid);
+
+    /* Sending and waiting */
+    gnrc_netapi_send(netif->pid, pkt);
+    gnrc_tx_sync(&tx_sync);
+
+    /* Cancel error message and send success message */
+    if (ztimer_remove(ZTIMER_SEC, &timer)) {
+        /* Successfully removed error message, not too late to send success */
+        msg_send(&success_msg, pid);
+    }
+
+    return 0;
+}

tests/net/gnrc_legacy_tx_sync/tests/01-run.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python3
+
+#  Copyright (C) 2025 Technische Universität Dresden
+#
+# This file is subject to the terms and conditions of the GNU Lesser
+# General Public License v2.1. See the file LICENSE in the top level
+# directory for more details.
+
+# @author      Lukas Luger <[email protected]>
+
+import sys
+from testrunner import run
+
+
+def testfunc(child):
+    child.expect("TEST PASSED", timeout=2)
+
+
+if __name__ == "__main__":
+    sys.exit(run(testfunc))