T8831: smoketests: irregular PermissionError caused by systemctl stop

Failures appear during PPPoEIf.remove() -> flush_addrs() -> set_dhcpv6(False),
where disable uses self._cmd(f'systemctl stop ...'), which raises on any
non-zero exit code of cmd().

PermissionError: [Errno 1] is misleading: cmd() raises OSError(exit_code,
feedback); exit code 1 maps to PermissionError in Python 3, so logs point at
"permissions" while the real signal is systemctl stop returned 1 (job failure,
timeout, restart contention with Restart=always on dhcp6c@.service.

Add a small systemd teardown helper stop_systemd_unit() validating the return
codes from the "systemctl stop" calls.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/services/vyos-netlinkd b/src/services/vyos-netlinkd
index c759ebd3d..7bf6b8cce 100755
--- a/src/services/vyos-netlinkd
+++ b/src/services/vyos-netlinkd
@@ -32,6 +32,7 @@ from vyos.utils.commit import commit_in_progress
 from vyos.utils.dict import dict_search
 from vyos.utils.process import cmd
 from vyos.utils.process import is_systemd_service_active
+from vyos.utils.process import stop_systemd_unit
 
 running = True
 
@@ -62,10 +63,10 @@ def _handle_dhcp_events(operstate: Optional[str], ifname: str) -> None:
         # Interface moved state to down
         if is_systemd_service_active(systemdV4_service):
             syslog.syslog(syslog.LOG_DEBUG, f'Stopping {systemdV4_service}...')
-            cmd(f'systemctl stop {systemdV4_service}')
+            stop_systemd_unit(systemdV4_service, raise_on_failure=False)
         if is_systemd_service_active(systemdV6_service):
             syslog.syslog(syslog.LOG_DEBUG, f'Stopping {systemdV6_service}...')
-            cmd(f'systemctl stop {systemdV6_service}')
+            stop_systemd_unit(systemdV6_service, raise_on_failure=False)
 
     elif operstate == 'UP':
         v6_restart = False