- if (h->u.g.busy) {
- /*
- * Just set the moribund flag, which will be noticed next
- * time an operation completes.
+ if (h->u.g.busy && h->type != HT_FOREIGN) {
+ /*
+ * If the handle is currently busy, we cannot immediately free
+ * it, because its subthread is in the middle of something.
+ * (Exception: foreign handles don't have a subthread.)
+ *
+ * Instead we must wait until it's finished its current
+ * operation, because otherwise the subthread will write to
+ * invalid memory after we free its context from under it. So
+ * we set the moribund flag, which will be noticed next time
+ * an operation completes.