[PATCH net-next v1 2/2] selftests: net: Add kthread preserving test in napi_threaded and busy_poll_test

@@ -127,6 +127,44 @@ def change_num_queues(cfg, nl) -> None:
     _assert_napi_threaded_enabled(nl, napi0_id)
     _assert_napi_threaded_enabled(nl, napi1_id)
 
+def nic_link_flap(cfg, nl) -> None:
+    """
+    Test that if threaded is enabled, and NIC goes through
+    a reset, the kthread stays unchanged across the link flap.
+    """
+    napis = nl.napi_get({'ifindex': cfg.ifindex}, dump=True)
+    ksft_ge(len(napis), 2)
+
+    napi0_id = napis[0]['id']
+    napi1_id = napis[1]['id']
+
+    _setup_deferred_cleanup(cfg)
+
+    # set threaded
+    _set_threaded_state(cfg, 1)
+    napis = nl.napi_get({'ifindex': cfg.ifindex}, dump=True)
+
+    # check napi threaded is set for both napis
+    _assert_napi_threaded_enabled(nl, napi0_id)
+    _assert_napi_threaded_enabled(nl, napi1_id)
+
+    pid0 = napis[0].get('pid')
+    pid1 = napis[1].get('pid')
+
+    cmd(f"ip link set {cfg.ifname} down")
+    cmd(f"ip link set {cfg.ifname} up")
+
+    # re-acquire napi info
+    napis = nl.napi_get({'ifindex': cfg.ifindex}, dump=True)
+    ksft_ge(len(napis), 2)
+
+    # check napi threaded is set for both napis
+    _assert_napi_threaded_enabled(nl, napi0_id)
+    _assert_napi_threaded_enabled(nl, napi1_id)
+
+    # check the kthread remains the same
+    ksft_eq(napis[0].get('pid'), pid0)
+    ksft_eq(napis[1].get('pid'), pid1)
 
 def main() -> None:
     """ Ksft boiler plate main """

@@ -134,7 +172,8 @@ def main() -> None:
     with NetDrvEnv(__file__, queue_count=2) as cfg:
         ksft_run([napi_init,
                   change_num_queues,
-                  enable_dev_threaded_disable_napi_threaded],
+                  enable_dev_threaded_disable_napi_threaded,
+                  nic_link_flap],
                  args=(cfg, NetdevFamily()))
     ksft_exit()
 

@@ -124,6 +124,23 @@ test_busypoll_with_napi_threaded()
 	return $?
 }
 
+test_busypoll_with_napi_threaded_link_flap()
+{
+	# Only enable napi threaded poll. Set suspend timeout and prefer busy
+	# poll to 0. Run again after a link flap.
+	test_busypoll 0 ${NAPI_THREADED_MODE_BUSY_POLL} 0 || return $?
+
+	ip netns exec nssv ip link set dev $NSIM_SV_NAME down
+	ip netns exec nscl ip link set dev $NSIM_CL_NAME down
+
+	ip netns exec nssv ip link set dev $NSIM_SV_NAME up
+	ip netns exec nscl ip link set dev $NSIM_CL_NAME up
+
+	test_busypoll 0 ${NAPI_THREADED_MODE_BUSY_POLL} 0
+
+	return $?
+}
+
 ###
 ### Code start
 ###

@@ -176,6 +193,13 @@ if [ $? -ne 0 ]; then
 	exit 1
 fi
 
+test_busypoll_with_napi_threaded_link_flap
+if [ $? -ne 0 ]; then
+	echo "test_busypoll_with_napi_threaded_link_flap failed"
+	cleanup_ns
+	exit 1
+fi
+
 echo "$NSIM_SV_FD:$NSIM_SV_IFIDX" > $NSIM_DEV_SYS_UNLINK
 
 echo $NSIM_CL_ID > $NSIM_DEV_SYS_DEL