MDEV Assertion `partition_id == m_extra_cache_part_id' failed in ha_partition::late_extra_no_cache

The problem was that multi_range_read_info_const() called
multi_range_key_create_key() which changed m_part_spec.start_part,
while there was an activ table scan ongoing.

Fixed by copying and restoring m_part_spec around
multi_range_key_create_calls()

mysql-test/suite/parts/r/cache.result

+CREATE TABLE t1 (f1 INT, f2 INT, f3 INT, f4 INT, KEY (f4), 
+KEY (f1,f4,f3,f2)
+) PARTITION BY RANGE(f1) ( PARTITION p VALUES LESS THAN MAXVALUE );
+INSERT IGNORE INTO t1 VALUES 
+(140,0,0,7),(143,92,NULL,0),(0,0,NULL,154),(NULL,255,117,197),(0,0,NULL,0),(60,0,0,1);
+CREATE TABLE t2 (f INT);
+INSERT INTO t2 VALUES (NULL),(35),(NULL),(2);
+SELECT * FROM t1, t2 WHERE f4 >= f;
+f1	f2	f3	f4	f
+0	0	NULL	154	2
+0	0	NULL	154	35
+140	0	0	7	2
+NULL	255	117	197	2
+NULL	255	117	197	35
+DROP TABLE t1, t2;

mysql-test/suite/parts/t/cache.test

+#
+# Test cases related to row cache
+#
+
+# The server must support partitioning.
+--source include/have_partition.inc
+
+CREATE TABLE t1 (f1 INT, f2 INT, f3 INT, f4 INT, KEY (f4), 
+  KEY (f1,f4,f3,f2)
+) PARTITION BY RANGE(f1) ( PARTITION p VALUES LESS THAN MAXVALUE );
+
+INSERT IGNORE INTO t1 VALUES 
+(140,0,0,7),(143,92,NULL,0),(0,0,NULL,154),(NULL,255,117,197),(0,0,NULL,0),(60,0,0,1);
+
+CREATE TABLE t2 (f INT);
+INSERT INTO t2 VALUES (NULL),(35),(NULL),(2);
+
+--sorted_result
+SELECT * FROM t1, t2 WHERE f4 >= f;
+
+# Cleanup
+DROP TABLE t1, t2;

sql/ha_partition.cc

@@ -5070,6 +5070,7 @@ int ha_partition::rnd_next(uchar *buf)
   }
 
 end:
+  DBUG_PRINT("exit", ("reset start_part"));
   m_part_spec.start_part= NO_CURRENT_PART_ID;
 end_dont_reset_start_part:
   DBUG_RETURN(result);
@@ -6223,10 +6224,13 @@ ha_rows ha_partition::multi_range_read_info_const(uint keyno,
   ha_rows rows= 0;
   uint ret_mrr_mode= 0;
   range_seq_t seq_it;
+  part_id_range save_part_spec;
   DBUG_ENTER("ha_partition::multi_range_read_info_const");
   DBUG_PRINT("enter", ("partition this: %p", this));
 
   m_mrr_new_full_buffer_size= 0;
+  save_part_spec= m_part_spec;
+
   seq_it= seq->init(seq_init_param, n_ranges, *mrr_mode);
   if ((error= multi_range_key_create_key(seq, seq_it)))
   {
@@ -6240,6 +6244,7 @@ ha_rows ha_partition::multi_range_read_info_const(uint keyno,
       (probably running out of memory) and we need to fallback to
       normal reads
     */
+    m_part_spec= save_part_spec;
     DBUG_RETURN(HA_POS_ERROR);
   }
   m_part_seq_if.get_key_info=
@@ -6269,7 +6274,10 @@ ha_rows ha_partition::multi_range_read_info_const(uint keyno,
                                     &m_mrr_buffer_size[i],
                                     &tmp_mrr_mode, cost);
       if (tmp_rows == HA_POS_ERROR)
+      {
+        m_part_spec= save_part_spec;
         DBUG_RETURN(HA_POS_ERROR);
+      }
       rows+= tmp_rows;
       ret_mrr_mode|= tmp_mrr_mode;
       m_mrr_new_full_buffer_size+= m_mrr_buffer_size[i];
@@ -6278,6 +6286,7 @@ ha_rows ha_partition::multi_range_read_info_const(uint keyno,
   *mrr_mode= ret_mrr_mode;
 
 calc_cost:
+  m_part_spec= save_part_spec;
   cost->reset();
   cost->avg_io_cost= 1;
   if ((*mrr_mode & HA_MRR_INDEX_ONLY) && rows > 2)
@@ -8660,8 +8669,8 @@ int ha_partition::extra(enum ha_extra_function operation)
   {
     if (!m_myisam)
       DBUG_RETURN(loop_extra(operation));
-    break;
   }
+  break;
 
   /* Category 3), used by MyISAM handlers */
   case HA_EXTRA_PREPARE_FOR_UPDATE: