Do not break the latching order in TRUNCATE TABLE.

dict_truncate_index_tree(): Replace parameter rec_t* rec with
btr_pcur_t* pcur.  Reposition pcur before calling btr_create().

sync_thread_add_level(): Remove the relaxation of the assertion added in r968.

dict/dict0crea.c

@@ -700,8 +700,10 @@ dict_truncate_index_tree(
 				/* out: new root page number, or
 				FIL_NULL on failure */
 	dict_table_t*	table,	/* in: the table the index belongs to */
-	rec_t*		rec,	/* in: record in the clustered index of
-				SYS_INDEXES table */
+	btr_pcur_t*	pcur,	/* in/out: persistent cursor pointing to
+				record in the clustered index of
+				SYS_INDEXES table. The cursor may be
+				repositioned in this call. */
 	mtr_t*		mtr)	/* in: mtr having the latch
 				on the record page. The mtr may be
 				committed and restarted in this call. */
@@ -710,6 +712,7 @@ dict_truncate_index_tree(
 	ulint		space;
 	ulint		type;
 	dulint		index_id;
+	rec_t*		rec;
 	byte*		ptr;
 	ulint		len;
 	ulint		comp;
@@ -720,6 +723,7 @@ dict_truncate_index_tree(
 #endif /* UNIV_SYNC_DEBUG */
 
 	ut_a(!dict_table_is_comp(dict_sys->sys_indexes));
+	rec = btr_pcur_get_rec(pcur);
 	ptr = rec_get_nth_field_old(rec, DICT_SYS_INDEXES_PAGE_NO_FIELD, &len);
 
 	ut_ad(len == 4);
@@ -785,10 +789,11 @@ dict_truncate_index_tree(
 	/* We will need to commit the mini-transaction in order to avoid
 	deadlocks in the btr_create() call, because otherwise we would
 	be freeing and allocating pages in the same mini-transaction. */
+	btr_pcur_store_position(pcur, mtr);
 	mtr_commit(mtr);
-	/* mtr_commit() will invalidate rec. */
-	rec = NULL;
+
 	mtr_start(mtr);
+	btr_pcur_restore_position(BTR_MODIFY_LEAF, pcur, mtr);
 
 	/* Find the index corresponding to this SYS_INDEXES record. */
 	for (index = UT_LIST_GET_FIRST(table->indexes);

include/dict0crea.h

@@ -62,8 +62,10 @@ dict_truncate_index_tree(
 				/* out: new root page number, or
 				FIL_NULL on failure */
 	dict_table_t*	table,	/* in: the table the index belongs to */
-	rec_t*		rec,	/* in: record in the clustered index of
-				SYS_INDEXES table */
+	btr_pcur_t*	pcur,	/* in/out: persistent cursor pointing to
+				record in the clustered index of
+				SYS_INDEXES table. The cursor may be
+				repositioned in this call. */
 	mtr_t*		mtr);	/* in: mtr having the latch
 				on the record page. The mtr may be
 				committed and restarted in this call. */

row/row0mysql.c

@@ -2820,12 +2820,10 @@ row_truncate_table_for_mysql(
 			goto next_rec;
 		}
 
-		btr_pcur_store_position(&pcur, &mtr);
+		/* This call may commit and restart mtr
+		and reposition pcur. */
+		root_page_no = dict_truncate_index_tree(table, &pcur, &mtr);
 
-		/* This call may commit and restart mtr. */
-		root_page_no = dict_truncate_index_tree(table, rec, &mtr);
-
-		btr_pcur_restore_position(BTR_MODIFY_LEAF, &pcur, &mtr);
 		rec = btr_pcur_get_rec(&pcur);
 
 		if (root_page_no != FIL_NULL) {

sync/sync0sync.c

@@ -1134,7 +1134,6 @@ sync_thread_add_level(
 		break;
 	case SYNC_TREE_NODE:
 		ut_a(sync_thread_levels_contain(array, SYNC_INDEX_TREE)
-		     || sync_thread_levels_contain(array, SYNC_DICT_OPERATION)
 		     || sync_thread_levels_g(array, SYNC_TREE_NODE - 1));
 		break;
 	case SYNC_TREE_NODE_NEW: