--- ddt.c	2010-06-25 15:30:21.084712659 +0200
+++ ddt.c.new	2010-06-25 15:30:16.980712010 +0200
@@ -964,10 +964,11 @@ ddt_repair_table(ddt_t *ddt, zio_t *rio)
 	avl_tree_t *t = &ddt->ddt_repair_tree;
 	blkptr_t blk;
 
+	ASSERT(MUTEX_HELD(&ddt->ddt_lock));
+
 	if (spa_sync_pass(spa) > 1)
 		return;
 
-	ddt_enter(ddt);
 	for (rdde = avl_first(t); rdde != NULL; rdde = rdde_next) {
 		rdde_next = AVL_NEXT(t, rdde);
 		avl_remove(&ddt->ddt_repair_tree, rdde);
@@ -978,7 +979,6 @@ ddt_repair_table(ddt_t *ddt, zio_t *rio)
 		ddt_repair_done(ddt, dde);
 		ddt_enter(ddt);
 	}
-	ddt_exit(ddt);
 }
 
 static void
@@ -1053,7 +1053,8 @@ ddt_sync_table(ddt_t *ddt, dmu_tx_t *tx,
 {
 	spa_t *spa = ddt->ddt_spa;
 	ddt_entry_t *dde;
-	void *cookie = NULL;
+
+	ASSERT(MUTEX_HELD(&ddt->ddt_lock));
 
 	if (avl_numnodes(&ddt->ddt_tree) == 0)
 		return;
@@ -1068,7 +1069,18 @@ ddt_sync_table(ddt_t *ddt, dmu_tx_t *tx,
 		    &spa->spa_ddt_stat_object, tx) == 0);
 	}
 
-	while ((dde = avl_destroy_nodes(&ddt->ddt_tree, &cookie)) != NULL) {
+	while ((dde = avl_first(&ddt->ddt_tree)) != NULL) {
+		if (dde->dde_loading) {
+			/*
+			 * If the entry is being loaded, wait for it.
+			 * Because we drop the ddt_lock during the wait,
+			 * we have to start over, as the entry might
+			 * have been removed in the meantime.
+			 */
+			cv_wait(&dde->dde_cv, &ddt->ddt_lock);
+			continue;
+		}
+		avl_remove(&ddt->ddt_tree, dde);
 		ddt_sync_entry(ddt, dde, tx, txg);
 		ddt_free(dde);
 	}
@@ -1106,8 +1118,10 @@ ddt_sync(spa_t *spa, uint64_t txg)
 		ddt_t *ddt = spa->spa_ddt[c];
 		if (ddt == NULL)
 			continue;
+		ddt_enter(ddt);
 		ddt_sync_table(ddt, tx, txg);
 		ddt_repair_table(ddt, rio);
+		ddt_exit(ddt);
 	}
 
 	(void) zio_wait(rio);