A fix and a test case for Bug#19399 "res 'Lost Connection' when

dropping/creating tables".

The bug could lead to a crash when multi-delete statements were
prepared and used with temporary tables.

The bug was caused by lack of clean-up of multi-delete tables before
re-execution of a prepared statement. In a statement like
DELETE t1 FROM t1, t2 WHERE ... the first table list (t1) is
moved to lex->auxilliary_table_list and excluded from lex->query_tables
or select_lex->tables. Thus it was unaccessible to reinit_stmt_before_use
and not cleaned up before re-execution of a prepared statement. 

mysql-test/r/ps.result

@@ -875,3 +875,17 @@ select @@max_prepared_stmt_count, @@prepared_stmt_count;
 @@max_prepared_stmt_count	@@prepared_stmt_count
 3	0
 set global max_prepared_stmt_count= @old_max_prepared_stmt_count;
+drop table if exists t1;
+create temporary table if not exists t1 (a1 int);
+prepare stmt from "delete t1 from t1 where (cast(a1/3 as unsigned) * 3) = a1";
+drop temporary table t1;
+create temporary table if not exists t1 (a1 int);
+execute stmt;
+drop temporary table t1;
+create temporary table if not exists t1 (a1 int);
+execute stmt;
+drop temporary table t1;
+create temporary table if not exists t1 (a1 int);
+execute stmt;
+drop temporary table t1;
+deallocate prepare stmt;

mysql-test/t/ps.test

@@ -926,4 +926,29 @@ select @@max_prepared_stmt_count, @@prepared_stmt_count;
 set global max_prepared_stmt_count= @old_max_prepared_stmt_count;
 --enable_ps_protocol
 
+#
+# Bug#19399 "Stored Procedures 'Lost Connection' when dropping/creating
+#            tables"
+# Check that multi-delete tables are also cleaned up before re-execution.
+# 
+--disable_warnings
+drop table if exists t1;
+create temporary table if not exists t1 (a1 int);
+--enable_warnings
+# exact delete syntax is essential
+prepare stmt from "delete t1 from t1 where (cast(a1/3 as unsigned) * 3) = a1";
+drop temporary table t1;
+create temporary table if not exists t1 (a1 int);
+# the server crashed on  the next statement without the fix
+execute stmt;
+drop temporary table t1;
+create temporary table if not exists t1 (a1 int);
+# the problem was in memory corruption: repeat the test just in case
+execute stmt;
+drop temporary table t1;
+create temporary table if not exists t1 (a1 int);
+execute stmt;
+drop temporary table t1;
+deallocate prepare stmt;
+
 # End of 4.1 tests

sql/sql_lex.cc

@@ -125,6 +125,7 @@ void lex_start(THD *thd, uchar *buf,uint length)
   lex->value_list.empty();
   lex->update_list.empty();
   lex->param_list.empty();
+  lex->auxilliary_table_list.empty();
   lex->unit.next= lex->unit.master=
     lex->unit.link_next= lex->unit.return_to= 0;
   lex->unit.prev= lex->unit.link_prev= 0;

sql/sql_prepare.cc

@@ -1727,14 +1727,9 @@ static void reset_stmt_for_execute(Prepared_statement *stmt)
 	 tables;
 	 tables= tables->next)
     {
-      /*
-        Reset old pointers to TABLEs: they are not valid since the tables
-        were closed in the end of previous prepare or execute call.
-      */
-      tables->table= 0;
-      tables->table_list= 0;
+      tables->reinit_before_use(thd);
     }
-    
+
     {
       SELECT_LEX_UNIT *unit= sl->master_unit();
       unit->unclean();
@@ -1743,6 +1738,17 @@ static void reset_stmt_for_execute(Prepared_statement *stmt)
       unit->reinit_exec_mechanism();
     }
   }
+  /*
+    Cleanup of the special case of DELETE t1, t2 FROM t1, t2, t3 ...
+    (multi-delete).  We do a full clean up, although at the moment all we
+    need to clean in the tables of MULTI-DELETE list is 'table' member.
+  */
+  for (TABLE_LIST *tables= (TABLE_LIST*) lex->auxilliary_table_list.first;
+       tables;
+       tables= tables->next)
+  {
+    tables->reinit_before_use(thd);
+  }
   lex->current_select= &lex->select_lex;
   if (lex->result)
     lex->result->cleanup();

sql/table.cc

@@ -1523,6 +1523,23 @@ db_type get_table_type(const char *name)
   DBUG_RETURN(ha_checktype((enum db_type) (uint) *(head+3)));
 }
 
+/*
+  Cleanup this table for re-execution.
+
+  SYNOPSIS
+    st_table_list::reinit_before_use()
+*/
+
+void st_table_list::reinit_before_use(THD * /* thd */)
+{
+  /*
+    Reset old pointers to TABLEs: they are not valid since the tables
+    were closed in the end of previous prepare or execute call.
+  */
+  table= 0;
+  table_list= 0;
+}
+
 
 /*****************************************************************************
 ** Instansiate templates

sql/table.h

@@ -238,6 +238,11 @@ typedef struct st_table_list
   bool		cacheable_table;	/* stop PS caching */
   /* used in multi-upd privelege check */
   bool		table_in_update_from_clause;
+  /*
+    Cleanup for re-execution in a prepared statement or a stored
+    procedure.
+  */
+  void reinit_before_use(THD *thd);
 } TABLE_LIST;
 
 typedef struct st_changed_table_list