core: do not spawn jobs or touch other units during coldplugging

Because the order of coldplugging is not defined, we can reference a
not-yet-coldplugged unit and read its state while it has not yet been
set to a meaningful value.

This way, already active units may get started again.

We fix this by deferring such actions until all units have been at
least somehow coldplugged.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=88401

1 files changed, 9 insertions, 3 deletions

diff --git a/src/core/unit.h b/src/core/unit.h
index ac5647a7f2..11242c2a00 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -301,8 +301,14 @@ struct UnitVTable {
         int (*load)(Unit *u);
 
         /* If a lot of units got created via enumerate(), this is
-         * where to actually set the state and call unit_notify(). */
-        int (*coldplug)(Unit *u);
+         * where to actually set the state and call unit_notify().
+         *
+         * This must not reference other units (maybe implicitly through spawning
+         * jobs), because it is possible that they are not yet coldplugged.
+         * Such actions must be deferred until the end of coldplug bу adding
+         * a "Unit* -> int(*)(Unit*)" entry into the hashmap.
+         */
+        int (*coldplug)(Unit *u, Hashmap *deferred_work);
 
         void (*dump)(Unit *u, FILE *f, const char *prefix);
 
@@ -538,7 +544,7 @@ int unit_deserialize(Unit *u, FILE *f, FDSet *fds);
 
 int unit_add_node_link(Unit *u, const char *what, bool wants);
 
-int unit_coldplug(Unit *u);
+int unit_coldplug(Unit *u, Hashmap *deferred_work);
 
 void unit_status_printf(Unit *u, const char *status, const char *unit_status_msg_format) _printf_(3, 0);