core: immediately trigger watchdog action on WATCHDOG=trigger

A service might be able to detect errors by itself that may require the
system to take the same action as if the service locked up. Add a
WATCHDOG=trigger state change notification to sd_notify() to let the
service manager know about the self-detected misery and instantly
trigger the configured watchdog behaviour.

2 files changed, 31 insertions, 2 deletions

diff --git a/man/sd_notify.xml b/man/sd_notify.xml
index 0084bf3882..00640cb290 100644
--- a/man/sd_notify.xml
+++ b/man/sd_notify.xml
@@ -174,6 +174,18 @@
       </varlistentry>
 
       <varlistentry>
+        <term>WATCHDOG=trigger</term>
+
+        <listitem><para>Tells the service manager that the service detected an internal error that should be handled by
+        the configured watchdog options. This will trigger the same behaviour as if <varname>WatchdogSec=</varname> is
+        enabled and the service did not send <literal>WATCHDOG=1</literal> in time. Note that
+        <varname>WatchdogSec=</varname> does not need to be enabled for <literal>WATCHDOG=trigger</literal> to trigger
+        the watchdog action. See
+        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
+        information about the watchdog behavior. </para></listitem>
+      </varlistentry>
+
+      <varlistentry>
         <term>WATCHDOG_USEC=…</term>
 
         <listitem><para>Reset <varname>watchdog_usec</varname> value during runtime.
diff --git a/src/core/service.c b/src/core/service.c
index c4d8378557..56667f03e8 100644
--- a/src/core/service.c
+++ b/src/core/service.c
@@ -3742,6 +3742,16 @@ static bool service_notify_message_authorized(Service *s, pid_t pid, char **tags
         return true;
 }
 
+static void service_force_watchdog(Service *s) {
+        if (!UNIT(s)->manager->service_watchdogs)
+                return;
+
+        log_unit_error(UNIT(s), "Watchdog request (last status: %s)!",
+                       s->status_text ? s->status_text : "<unset>");
+
+        service_enter_signal(s, SERVICE_STOP_WATCHDOG, SERVICE_FAILURE_WATCHDOG);
+}
+
 static void service_notify_message(
                 Unit *u,
                 const struct ucred *ucred,
@@ -3888,8 +3898,15 @@ static void service_notify_message(
         }
 
         /* Interpret WATCHDOG= */
-        if (strv_find(tags, "WATCHDOG=1"))
-                service_reset_watchdog(s);
+        e = strv_find_startswith(tags, "WATCHDOG=");
+        if (e) {
+                if (streq(e, "1"))
+                        service_reset_watchdog(s);
+                else if (streq(e, "trigger"))
+                        service_force_watchdog(s);
+                else
+                        log_unit_warning(u, "Passed WATCHDOG= field is invalid, ignoring.");
+        }
 
         e = strv_find_startswith(tags, "WATCHDOG_USEC=");
         if (e) {