TEST-17: add reproducer for issue #35329

Without the previous commit, the test case will fail.

test/units/TEST-17-UDEV.device_is_processing.sh

@@ -0,0 +1,71 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: LGPL-2.1-or-later
+# shellcheck disable=SC2317
+set -ex
+set -o pipefail
+
+# This is a reproducer of issue #35329,
+# which is a regression caused by 405be62f05d76f1845f347737b5972158c79dd3e.
+
+IFNAME=udevtestnetif
+
+at_exit() {
+    set +e
+
+    systemctl stop testsleep.service
+    rm -f /run/udev/udev.conf.d/timeout.conf
+    rm -f /run/udev/rules.d/99-testsuite.rules
+    # Forcibly kills sleep command invoked by the udev rule before restarting,
+    # otherwise systemctl restart below will takes longer.
+    killall -KILL sleep
+    systemctl restart systemd-udevd.service
+    ip link del "$IFNAME"
+}
+
+trap at_exit EXIT
+
+udevadm settle
+
+mkdir -p /run/udev/udev.conf.d/
+cat >/run/udev/udev.conf.d/timeout.conf <<EOF
+event_timeout=1h
+EOF
+
+mkdir -p /run/udev/rules.d/
+cat >/run/udev/rules.d/99-testsuite.rules <<EOF
+SUBSYSTEM=="net", ACTION=="change", KERNEL=="${IFNAME}", OPTIONS="log_level=debug", RUN+="/usr/bin/sleep 1000"
+EOF
+
+systemctl restart systemd-udevd.service
+
+ip link add "$IFNAME" type dummy
+IFINDEX=$(ip -json link show "$IFNAME" | jq '.[].ifindex')
+udevadm wait --timeout 10 "/sys/class/net/${IFNAME}"
+# Check if the database file is created.
+[[ -e "/run/udev/data/n${IFINDEX}" ]]
+
+systemd-run \
+    -p After="sys-subsystem-net-devices-${IFNAME}.device" \
+    -p BindsTo="sys-subsystem-net-devices-${IFNAME}.device" \
+    -u testsleep.service \
+    sleep 1h
+
+timeout 10 bash -c 'until systemctl is-active testsleep.service; do sleep .5; done'
+
+udevadm trigger "/sys/class/net/${IFNAME}"
+timeout 30 bash -c "until grep -F 'ID_PROCESSING=1' /run/udev/data/n${IFINDEX}; do sleep .5; done"
+
+for _ in {1..3}; do
+    systemctl daemon-reexec
+    systemctl is-active testsleep.service
+done
+
+for _ in {1..3}; do
+    systemctl daemon-reload
+    systemctl is-active testsleep.service
+done
+
+# Check if the reexec and reload have finished during processing the event.
+grep -F 'ID_PROCESSING=1' "/run/udev/data/n${IFINDEX}"
+
+exit 0