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, 12 insertions, 2 deletions

diff --git a/src/login/logind.c b/src/login/logind.c
index 48da7b173b..a6f84e8536 100644
--- a/src/login/logind.c
+++ b/src/login/logind.c
@@ -871,8 +871,15 @@ void manager_gc(Manager *m, bool drop_not_started) {
                 LIST_REMOVE(gc_queue, m->session_gc_queue, session);
                 session->in_gc_queue = false;
 
-                if (!session_check_gc(session, drop_not_started)) {
+                /* First, if we are not closing yet, initiate stopping */
+                if (!session_check_gc(session, drop_not_started) &&
+                    session_get_state(session) != SESSION_CLOSING)
                         session_stop(session);
+
+                /* Normally, this should make the session busy again,
+                 * if it doesn't then let's get rid of it
+                 * immediately */
+                if (!session_check_gc(session, drop_not_started)) {
                         session_finalize(session);
                         session_free(session);
                 }
@@ -882,8 +889,11 @@ void manager_gc(Manager *m, bool drop_not_started) {
                 LIST_REMOVE(gc_queue, m->user_gc_queue, user);
                 user->in_gc_queue = false;
 
-                if (!user_check_gc(user, drop_not_started)) {
+                if (!user_check_gc(user, drop_not_started) &&
+                    user_get_state(user) != USER_CLOSING)
                         user_stop(user);
+
+                if (!user_check_gc(user, drop_not_started)) {
                         user_finalize(user);
                         user_free(user);
                 }