+/*
+ * Deadlist concurrency:
+ *
+ * Deadlists can only be modified from the syncing thread.
+ *
+ * Except for dsl_deadlist_insert(), it can only be modified with the
+ * dp_config_rwlock held with RW_WRITER.
+ *
+ * The accessors (dsl_deadlist_space() and dsl_deadlist_space_range()) can
+ * be called concurrently, from open context, with the dl_config_rwlock held
+ * with RW_READER.
+ *
+ * Therefore, we only need to provide locking between dsl_deadlist_insert() and
+ * the accessors, protecting:
+ * dl_phys->dl_used,comp,uncomp
+ * and protecting the dl_tree from being loaded.
+ * The locking is provided by dl_lock. Note that locking on the bpobj_t
+ * provides its own locking, and dl_oldfmt is immutable.
+ */
+