tests: bsim: bluetooth: host: robust subscription proc

GATT subscription in conn_stress test was failing and stalling the test
due to lack of TX buffers. Retry mechanism added as a workaround.

Removing this workaround would make the test fail due to deadlocks,
and require allocating more buffers with CONFIG_BT_L2CAP_TX_BUF_COUNT
set to 10 as a workaround.

Signed-off-by: Artur Dobrynin <[email protected]>

Author: ardo-nordic

tests/bsim/bluetooth/host/misc/conn_stress/central/prj.conf

@@ -22,10 +22,6 @@ CONFIG_ASSERT_LEVEL=2
 CONFIG_ASSERT_VERBOSE=y
 CONFIG_ASSERT_ON_ERRORS=y
 
-# TODO: use default 3
-# we get an ATT timeout if 3 or SMP timeout if 10
-CONFIG_BT_L2CAP_TX_BUF_COUNT=10
-
 # deadlock on central with the default.
 # the problem is that `tx_free` is called from both syswq and btwq in that case.
 CONFIG_BT_RECV_WORKQ_BT=y

tests/bsim/bluetooth/host/misc/conn_stress/central/src/main.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023 Nordic Semiconductor ASA
+ * Copyright (c) 2023-2025 Nordic Semiconductor ASA
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -22,7 +22,7 @@
 #include <zephyr/types.h>
 
 #include <zephyr/logging/log.h>
-LOG_MODULE_REGISTER(central, LOG_LEVEL_DBG);
+LOG_MODULE_REGISTER(central, LOG_LEVEL_INF);
 
 #include "bstests.h"
 #include "bs_types.h"
@@ -73,6 +73,7 @@ enum {
 	CONN_INFO_MTU_EXCHANGED,
 	CONN_INFO_DISCOVERING,
 	CONN_INFO_DISCOVER_PAUSED,
+	CONN_INFO_SUBSCRIPTION_FAILED,
 	CONN_INFO_SUBSCRIBED,
 
 	/* Total number of flags - must be at the end of the enum */
@@ -213,6 +214,24 @@ static uint8_t notify_func(struct bt_conn *conn, struct bt_gatt_subscribe_params
 	return BT_GATT_ITER_CONTINUE;
 }
 
+static void subscribe_func(struct bt_conn *conn, uint8_t err,
+			      struct bt_gatt_subscribe_params *params)
+{
+	struct conn_info *conn_info_ref;
+	char addr[BT_ADDR_LE_STR_LEN];
+
+	bt_addr_le_to_str(bt_conn_get_dst(conn), addr, sizeof(addr));
+	__ASSERT(!err, "Subscribe failed for addr %s (err %d)", addr, err);
+
+	conn_info_ref = get_conn_info_ref(conn);
+	__ASSERT_NO_MSG(conn_info_ref);
+
+	atomic_clear_bit(conn_info_ref->flags, CONN_INFO_SUBSCRIPTION_FAILED);
+	atomic_set_bit(conn_info_ref->flags, CONN_INFO_SUBSCRIBED);
+
+	LOG_DBG("[SUBSCRIBED] addr %s", addr);
+}
+
 static uint8_t discover_func(struct bt_conn *conn, const struct bt_gatt_attr *attr,
 			     struct bt_gatt_discover_params *params)
 {
@@ -248,6 +267,7 @@ static uint8_t discover_func(struct bt_conn *conn, const struct bt_gatt_attr *at
 
 		err = bt_gatt_discover(conn, &conn_info_ref->discover_params);
 		if (err == -ENOMEM || err == -ENOTCONN) {
+			atomic_set_bit(conn_info_ref->flags, CONN_INFO_DISCOVER_PAUSED);
 			goto retry;
 		}
 
@@ -263,33 +283,27 @@ static uint8_t discover_func(struct bt_conn *conn, const struct bt_gatt_attr *at
 
 		err = bt_gatt_discover(conn, &conn_info_ref->discover_params);
 		if (err == -ENOMEM || err == -ENOTCONN) {
+			atomic_set_bit(conn_info_ref->flags, CONN_INFO_DISCOVER_PAUSED);
 			goto retry;
 		}
 
 		__ASSERT(!err, "Discover failed (err %d)", err);
 
 	} else {
 		conn_info_ref->subscribe_params.notify = notify_func;
+		conn_info_ref->subscribe_params.subscribe = subscribe_func;
 		conn_info_ref->subscribe_params.value = BT_GATT_CCC_NOTIFY;
 		conn_info_ref->subscribe_params.ccc_handle = attr->handle;
 
 		err = bt_gatt_subscribe(conn, &conn_info_ref->subscribe_params);
-		if (err == -ENOMEM || err == -ENOTCONN) {
+		if (err == -ENOMEM || err == -ENOTCONN || err == -EALREADY) {
+			LOG_DBG("Subcription failed (err %d)", err);
+			atomic_set_bit(conn_info_ref->flags, CONN_INFO_SUBSCRIPTION_FAILED);
 			goto retry;
 		}
 
-		if (err != -EALREADY) {
-			__ASSERT(!err, "Subscribe failed (err %d)", err);
-		}
-
 		__ASSERT_NO_MSG(atomic_test_bit(conn_info_ref->flags, CONN_INFO_DISCOVERING));
 		__ASSERT_NO_MSG(!atomic_test_bit(conn_info_ref->flags, CONN_INFO_SUBSCRIBED));
-		atomic_set_bit(conn_info_ref->flags, CONN_INFO_SUBSCRIBED);
-
-		char addr[BT_ADDR_LE_STR_LEN];
-
-		bt_addr_le_to_str(bt_conn_get_dst(conn), addr, sizeof(addr));
-		LOG_INF("[SUBSCRIBED] addr %s", addr);
 	}
 
 	return BT_GATT_ITER_STOP;
@@ -299,7 +313,6 @@ static uint8_t discover_func(struct bt_conn *conn, const struct bt_gatt_attr *at
 	 * later.
 	 */
 	LOG_INF("out of memory/not connected, continuing sub later (err %d)", err);
-	atomic_set_bit(conn_info_ref->flags, CONN_INFO_DISCOVER_PAUSED);
 
 	return BT_GATT_ITER_STOP;
 }
@@ -579,6 +592,18 @@ static void subscribe_to_service(struct bt_conn *conn, void *data)
 		return;
 	}
 
+	/* If subcription attempt failed before (due to most likely lack of TX buffers),
+	 *  make a new attempt here.
+	 */
+	if (atomic_test_bit(conn_info_ref->flags, CONN_INFO_SUBSCRIPTION_FAILED)) {
+		err = bt_gatt_subscribe(conn, &conn_info_ref->subscribe_params);
+		if (err != -ENOMEM) {
+			__ASSERT(!err, "Subcription failed");
+		} else {
+			return;
+		}
+	}
+
 	/* start subscription procedure if:
 	 * - we haven't started it yet for this conn
 	 * - it was suspended due to a lack of resources
@@ -724,7 +749,7 @@ void test_init(void)
 	extern enum bst_result_t bst_result;
 
 	LOG_INF("Initializing Test");
-	bst_ticker_set_next_tick_absolute(600*1e6);
+	bst_ticker_set_next_tick_absolute(100*1e6);
 	/* The peripherals determines whether the test passed. */
 	bst_result = Passed;
 }

tests/bsim/bluetooth/host/misc/conn_stress/peripheral/src/main.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023 Nordic Semiconductor ASA
+ * Copyright (c) 2023-2025 Nordic Semiconductor ASA
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -24,7 +24,7 @@
 #include <zephyr/types.h>
 
 #include <zephyr/logging/log.h>
-LOG_MODULE_REGISTER(peripheral, LOG_LEVEL_DBG);
+LOG_MODULE_REGISTER(peripheral, LOG_LEVEL_INF);
 
 #include "bstests.h"
 #include "bs_types.h"
@@ -424,7 +424,7 @@ void test_peripheral_main(void)
 		LOG_ERR("Advertising failed to start (err %d)", err);
 		__ASSERT_NO_MSG(err);
 	}
-	LOG_DBG("Started advertising");
+	LOG_INF("Started advertising");
 
 	bt_gatt_cb_register(&gatt_callbacks);
 
@@ -449,7 +449,7 @@ void test_peripheral_main(void)
 			k_sleep(K_MSEC(10));
 		}
 
-		LOG_DBG("Begin sending notifications to central..");
+		LOG_INF("Begin sending notifications to central..");
 		while (central_subscription &&
 		       atomic_test_bit(conn_info.flags, CONN_INFO_CONNECTED)) {
 
@@ -468,7 +468,7 @@ void test_peripheral_main(void)
 
 			if (atomic_get(&conn_info.tx_notify_counter) > MIN_NOTIFICATIONS &&
 			    atomic_get(&conn_info.notify_counter) > MIN_NOTIFICATIONS) {
-				LOG_DBG("Disconnecting..");
+				LOG_INF("Disconnecting..");
 				disconnect();
 			}
 		}
@@ -482,7 +482,7 @@ void test_init(void)
 	extern enum bst_result_t bst_result;
 
 	LOG_INF("Initializing Test");
-	bst_ticker_set_next_tick_absolute(600*1e6);
+	bst_ticker_set_next_tick_absolute(100*1e6);
 	bst_result = Failed;
 }
 

tests/bsim/bluetooth/host/misc/conn_stress/scripts/conn_stress.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# Copyright (c) 2023 Nordic Semiconductor
+# Copyright (c) 2023-2025 Nordic Semiconductor
 # SPDX-License-Identifier: Apache-2.0
 
 source ${ZEPHYR_BASE}/tests/bsim/sh_common.source
@@ -9,9 +9,11 @@ simulation_id="conn_stress"
 test_path="tests_bsim_bluetooth_host_misc_conn_stress"
 bsim_central_exe_name="bs_${BOARD_TS}_${test_path}_central_prj_conf"
 bsim_peripheral_exe_name="bs_${BOARD_TS}_${test_path}_peripheral_prj_conf"
-bsim_args="-RealEncryption=1 -v=5 -s=${simulation_id}"
+bsim_args="-RealEncryption=1 -v=2 -s=${simulation_id}"
 test_args="-argstest notify_size=220 conn_interval=32"
 
+EXECUTE_TIMEOUT=120
+
 cd ${BSIM_OUT_PATH}/bin
 
 for device in `seq 1 12`; do
@@ -21,8 +23,8 @@ for device in `seq 1 12`; do
         -d=$device -rs=$rs -testid=peripheral ${test_args}
 done
 
-Execute "./${bsim_central_exe_name}" ${bsim_args} -d=0 -rs=001 -testid=central ${test_args}
+Execute "./${bsim_central_exe_name}" ${bsim_args} -d=0 -rs=1 -testid=central ${test_args}
 
-Execute ./bs_2G4_phy_v1 -dump -v=2 -s=${simulation_id} -D=13 -sim_length=10000e6 &
+Execute ./bs_2G4_phy_v1 -dump -v=2 -s=${simulation_id} -D=13 -sim_length=100e6
 
 wait_for_background_jobs