logind: rework session shutdown logic

Simplify the shutdown logic a bit:

- Keep the session FIFO around in the PAM module, even after the session
  shutdown hook has been finished. This allows logind to track precisely
  when the PAM handler goes away.

- In the ReleaseSession() call start a timer, that will stop terminate
  the session when elapsed.

- Never fiddle with the KillMode of scopes to configure whether user
  processes should be killed or not. Instead, simply leave the scope
  units around when we terminate a session whose processes should not be
  killed.

- When killing is enabled, stop the session scope on FIFO EOF or after
  the ReleaseSession() timeout. When killing is disabled, simply tell
  PID 1 to abandon the scope.

Because the scopes stay around and hence all processes are always member
of a scope, the system shutdown logic should be more robust, as the
scopes can be shutdown as part of the usual shutdown logic.

1 files changed, 15 insertions, 8 deletions

diff --git a/src/login/logind-user.c b/src/login/logind-user.c
index bdb691563..fdbf6e3aa 100644
--- a/src/login/logind-user.c
+++ b/src/login/logind-user.c
@@ -515,6 +515,8 @@ int user_stop(User *u) {
         if (k < 0)
                 r = k;
 
+        u->stopping = true;
+
         user_save(u);
 
         return r;
@@ -633,22 +635,27 @@ void user_add_to_gc_queue(User *u) {
 
 UserState user_get_state(User *u) {
         Session *i;
-        bool all_closing = true;
 
         assert(u);
 
+        if (u->stopping)
+                return USER_CLOSING;
+
         if (u->slice_job || u->service_job)
                 return USER_OPENING;
 
-        LIST_FOREACH(sessions_by_user, i, u->sessions) {
-                if (session_is_active(i))
-                        return USER_ACTIVE;
-                if (session_get_state(i) != SESSION_CLOSING)
-                        all_closing = false;
-        }
+        if (u->sessions) {
+                bool all_closing = true;
+
+                LIST_FOREACH(sessions_by_user, i, u->sessions) {
+                        if (session_is_active(i))
+                                return USER_ACTIVE;
+                        if (session_get_state(i) != SESSION_CLOSING)
+                                all_closing = false;
+                }
 
-        if (u->sessions)
                 return all_closing ? USER_CLOSING : USER_ONLINE;
+        }
 
         if (user_check_linger_file(u) > 0)
                 return USER_LINGERING;