diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c
index d347c5b91c..1575cc1b41 100644
--- a/module/zfs/dbuf.c
+++ b/module/zfs/dbuf.c
@@ -1300,6 +1300,11 @@ dbuf_unoverride(dbuf_dirty_record_t *dr)
 	uint64_t txg = dr->dr_txg;
 
 	ASSERT(MUTEX_HELD(&db->db_mtx));
+	/*
+	 * This assert is valid because dmu_sync() expects to be called by
+	 * a zilog's get_data while holding a range lock.  This call only
+	 * comes from dbuf_dirty() callers who must also hold a range lock.
+	 */
 	ASSERT(dr->dt.dl.dr_override_state != DR_IN_DMU_SYNC);
 	ASSERT(db->db_level == 0);
 
diff --git a/module/zfs/dsl_scan.c b/module/zfs/dsl_scan.c
index 5b52681d8d..89faaeb8f0 100644
--- a/module/zfs/dsl_scan.c
+++ b/module/zfs/dsl_scan.c
@@ -1511,6 +1511,7 @@ dsl_scan_active(dsl_scan_t *scn)
 	return (used != 0);
 }
 
+/* Called whenever a txg syncs. */
 void
 dsl_scan_sync(dsl_pool_t *dp, dmu_tx_t *tx)
 {
@@ -1956,6 +1957,7 @@ dsl_scan_scrub_cb(dsl_pool_t *dp,
 	return (0);
 }
 
+/* Called by the ZFS_IOC_POOL_SCAN ioctl to start a scrub or resilver */
 int
 dsl_scan(dsl_pool_t *dp, pool_scan_func_t func)
 {