service: stop/reset watchdog on freeze/thaw

Otherwise the unit will be killed by the watchdog given it's frozen
but the clock keeps ticking

Fixes https://github.com/systemd/systemd/issues/38517

src/core/service.c

@@ -5636,6 +5636,22 @@ int service_determine_exec_selinux_label(Service *s, char **ret) {
         return 0;
 }
 
+static int service_cgroup_freezer_action(Unit *u, FreezerAction action) {
+        Service *s = ASSERT_PTR(SERVICE(u));
+        int r;
+
+        r = unit_cgroup_freezer_action(u, action);
+        if (r <= 0)
+                return r;
+
+        if (action == FREEZER_FREEZE)
+                service_stop_watchdog(s);
+        else if (action == FREEZER_THAW)
+                service_reset_watchdog(s);
+
+        return r;
+}
+
 static const char* const service_restart_table[_SERVICE_RESTART_MAX] = {
         [SERVICE_RESTART_NO]          = "no",
         [SERVICE_RESTART_ON_SUCCESS]  = "on-success",
@@ -5773,7 +5789,7 @@ const UnitVTable service_vtable = {
         .live_mount = service_live_mount,
         .can_live_mount = service_can_live_mount,
 
-        .freezer_action = unit_cgroup_freezer_action,
+        .freezer_action = service_cgroup_freezer_action,
 
         .serialize = service_serialize,
         .deserialize_item = service_deserialize_item,

test/units/TEST-38-FREEZER.sh

@@ -360,6 +360,26 @@ testcase_preserve_state() {
     echo
 }
 
+testcase_watchdog() {
+    local unit="wd.service"
+
+    systemd-run --collect --unit "$unit" --property WatchdogSec=4s --property Type=notify \
+        /bin/bash -c 'systemd-notify --ready; while true; do systemd-notify WATCHDOG=1; sleep 1; done'
+
+    systemctl freeze "$unit"
+
+    check_freezer_state "$unit" "frozen"
+    sleep 6
+    check_freezer_state "$unit" "frozen"
+
+    systemctl thaw "$unit"
+    sleep 6
+    check_freezer_state "$unit" "running"
+    systemctl is-active "$unit"
+
+    systemctl stop "$unit"
+}
+
 if [[ -e /sys/fs/cgroup/system.slice/cgroup.freeze ]]; then
     start_test_service
     run_testcases