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, 33 insertions, 2 deletions

diff --git a/src/core/manager.c b/src/core/manager.c
index 7a6d5190e7..3e87aa969b 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -975,7 +975,28 @@ static int manager_coldplug(Manager *m) {
         Unit *u;
         char *k;
 
-        assert(m);
+        /*
+         * Some unit types tend to spawn jobs or check other units' state
+         * during coldplug. This is wrong because it is undefined whether the
+         * units in question have been already coldplugged (i. e. their state
+         * restored). This way, we can easily re-start an already started unit
+         * or otherwise make a wrong decision based on the unit's state.
+         *
+         * Solve this by providing a way for coldplug functions to defer
+         * such actions until after all units have been coldplugged.
+         *
+         * We store Unit* -> int(*)(Unit*).
+         *
+         * https://bugs.freedesktop.org/show_bug.cgi?id=88401
+         */
+        _cleanup_hashmap_free_ Hashmap *deferred_work = NULL;
+        int(*proc)(Unit*);
+
+        assert(m);
+
+        deferred_work = hashmap_new(&trivial_hash_ops);
+        if (!deferred_work)
+                return -ENOMEM;
 
         /* Then, let's set up their initial state. */
         HASHMAP_FOREACH_KEY(u, k, m->units, i) {
@@ -985,7 +1006,17 @@ static int manager_coldplug(Manager *m) {
                 if (u->id != k)
                         continue;
 
-                q = unit_coldplug(u);
+                q = unit_coldplug(u, deferred_work);
+                if (q < 0)
+                        r = q;
+        }
+
+        /* After coldplugging and setting up initial state of the units,
+         * let's perform operations which spawn jobs or query units' state. */
+        HASHMAP_FOREACH_KEY(proc, u, deferred_work, i) {
+                int q;
+
+                q = proc(u);
                 if (q < 0)
                         r = q;
         }