Applied the fix for bug #51084 taken from a mysql tree.

mysql-test/r/join_cache.result

@@ -5173,7 +5173,6 @@ a	b
 2	2
 set join_cache_level=default;
 drop table t1,t2,t3;
-set @@optimizer_switch=@save_optimizer_switch;
 #
 # Bug #52394:  using join buffer for 3 table join with ref access 
 # LP #623209: and no references to the columns of the middle table
@@ -5202,3 +5201,45 @@ a
 27
 DROP TABLE t1,t2,t3;
 set join_cache_level=default;
+#
+# Bug#51084: Batched key access crashes for SELECT with
+#            derived table and LEFT JOIN 
+#
+CREATE TABLE t1 (
+carrier int,
+id int PRIMARY KEY
+);
+INSERT INTO t1 VALUES (1,11),(1,12),(2,13);
+CREATE TABLE t2 (
+scan_date int,
+package_id int
+);
+INSERT INTO t2 VALUES (2008,21),(2008,22);
+CREATE TABLE t3 (
+carrier int PRIMARY KEY,
+id int
+);
+INSERT INTO t3 VALUES (1,31);
+CREATE TABLE t4 (
+carrier_id int,
+INDEX carrier_id(carrier_id)
+);
+INSERT INTO t4 VALUES (31),(32);
+SET join_cache_level=8;
+SELECT COUNT(*)
+FROM (t2 JOIN t1) LEFT JOIN (t3 JOIN t4 ON t3.id = t4.carrier_id)
+ON t3.carrier = t1.carrier;
+COUNT(*)
+6
+EXPLAIN
+SELECT COUNT(*)
+FROM (t2 JOIN t1) LEFT JOIN (t3 JOIN t4 ON t3.id = t4.carrier_id)
+ON t3.carrier = t1.carrier;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3	Using join buffer
+1	SIMPLE	t3	eq_ref	PRIMARY	PRIMARY	4	test.t1.carrier	1	
+1	SIMPLE	t4	ref	carrier_id	carrier_id	5	test.t3.id	2	Using index
+SET join_cache_level=default;
+DROP TABLE t1,t2,t3,t4;
+set @@optimizer_switch=@save_optimizer_switch;

mysql-test/t/join_cache.test

@@ -1955,8 +1955,6 @@ set join_cache_level=default;
 
 drop table t1,t2,t3;
 
-set @@optimizer_switch=@save_optimizer_switch;
-
 --echo #
 --echo # Bug #52394:  using join buffer for 3 table join with ref access 
 --echo # LP #623209: and no references to the columns of the middle table
@@ -1984,3 +1982,49 @@ DROP TABLE t1,t2,t3;
 
 set join_cache_level=default;
 
+--echo #
+--echo # Bug#51084: Batched key access crashes for SELECT with
+--echo #            derived table and LEFT JOIN 
+--echo #
+
+CREATE TABLE t1 (
+  carrier int,
+  id int PRIMARY KEY
+);
+INSERT INTO t1 VALUES (1,11),(1,12),(2,13);
+
+CREATE TABLE t2 (
+  scan_date int,
+  package_id int
+);
+INSERT INTO t2 VALUES (2008,21),(2008,22);
+
+CREATE TABLE t3 (
+  carrier int PRIMARY KEY,
+  id int
+);
+INSERT INTO t3 VALUES (1,31);
+
+CREATE TABLE t4 (
+  carrier_id int,
+  INDEX carrier_id(carrier_id)
+);
+INSERT INTO t4 VALUES (31),(32);
+
+SET join_cache_level=8;
+
+SELECT COUNT(*)
+  FROM (t2 JOIN t1) LEFT JOIN (t3 JOIN t4 ON t3.id = t4.carrier_id)
+       ON t3.carrier = t1.carrier;
+
+EXPLAIN
+SELECT COUNT(*)
+  FROM (t2 JOIN t1) LEFT JOIN (t3 JOIN t4 ON t3.id = t4.carrier_id)
+       ON t3.carrier = t1.carrier;
+
+SET join_cache_level=default;
+
+DROP TABLE t1,t2,t3,t4;
+
+# this must be the last command in the file
+set @@optimizer_switch=@save_optimizer_switch;

sql/sql_select.cc

@@ -7202,6 +7202,19 @@ void set_join_cache_denial(JOIN_TAB *join_tab)
 {
   if (join_tab->cache)
   {
+    /* 
+      If there is a previous cache linked to this cache through the
+      next_cache pointer: remove the link. 
+    */
+    if (join_tab->cache->prev_cache)
+      join_tab->cache->prev_cache->next_cache= 0;
+    /*
+      No need to do the same for next_cache since cache denial is done
+      backwards starting from the latest cache in the linked list (see
+      revise_cache_usage()).
+    */
+    DBUG_ASSERT(!join_tab->cache->next_cache);
+
     join_tab->cache->free();
     join_tab->cache= 0;
   }