Fixed BUG#4579: Execution of SP crashes server.

Sub-CALLs of procedures zapped thd->current_arena for good.

mysql-test/r/sp.result

@@ -1387,6 +1387,27 @@ group_concat(v)
 yz,yz
 drop procedure bug3368|
 drop table t3|
+drop table if exists t3|
+create table t3 (f1 int, f2 int);
+insert into t3 values (1,1);
+create procedure bug4579_1 ()
+begin
+declare sf1 int;
+select f1 into sf1 from t3 where f1=1 and f2=1;
+update t3 set f2 = f2 + 1 where f1=1 and f2=1;
+call bug4579_2();
+end|
+create procedure bug4579_2 ()
+begin
+end|
+call bug4579_1()|
+call bug4579_1()|
+Warnings:
+call bug4579_1()|
+Warnings:
+drop procedure bug4579_1|
+drop procedure bug4579_2|
+drop table t3|
 drop table if exists fac|
 create table fac (n int unsigned not null primary key, f bigint unsigned)|
 create procedure ifac(n int unsigned)

mysql-test/t/sp.test

@@ -1592,6 +1592,36 @@ call bug3368('yz')|
 drop procedure bug3368|
 drop table t3|
 
+#
+# BUG#4579
+#
+--disable_warnings
+drop table if exists t3|
+--enable_warnings
+create table t3 (f1 int, f2 int);
+insert into t3 values (1,1);
+
+create procedure bug4579_1 ()
+begin
+  declare sf1 int;
+
+  select f1 into sf1 from t3 where f1=1 and f2=1;
+  update t3 set f2 = f2 + 1 where f1=1 and f2=1;
+  call bug4579_2();
+end|
+
+create procedure bug4579_2 ()
+begin
+end|
+
+call bug4579_1()|
+call bug4579_1()|
+call bug4579_1()|
+
+drop procedure bug4579_1|
+drop procedure bug4579_2|
+drop table t3|
+
 
 #
 # Some "real" examples

sql/sp_head.cc

@@ -377,9 +377,11 @@ sp_head::execute(THD *thd)
   DBUG_ENTER("sp_head::execute");
   char olddb[128];
   bool dbchanged;
-  sp_rcontext *ctx= thd->spcont;
+  sp_rcontext *ctx;
   int ret= 0;
   uint ip= 0;
+  Item_arena *old_arena;
+
 
 #ifndef EMBEDDED_LIBRARY
   if (check_stack_overrun(thd, olddb))
@@ -392,10 +394,12 @@ sp_head::execute(THD *thd)
   if ((ret= sp_use_new_db(thd, m_db.str, olddb, sizeof(olddb), 0, &dbchanged)))
     goto done;
 
-  if (ctx)
+  if ((ctx= thd->spcont))
     ctx->clear_handler();
   thd->query_error= 0;
+  old_arena= thd->current_arena;
   thd->current_arena= this;
+
   do
   {
     sp_instr *i;
@@ -433,14 +437,14 @@ sp_head::execute(THD *thd)
   } while (ret == 0 && !thd->killed && !thd->query_error &&
 	   !thd->net.report_error);
 
+  if (thd->current_arena)
+    cleanup_items(thd->current_arena->free_list);
+  thd->current_arena= old_arena;
+
  done:
   DBUG_PRINT("info", ("ret=%d killed=%d query_error=%d",
 		      ret, thd->killed, thd->query_error));
 
-  if (thd->current_arena)
-    cleanup_items(thd->current_arena->free_list);
-  thd->current_arena= 0;
-
   if (thd->killed || thd->query_error || thd->net.report_error)
     ret= -1;
   /* If the DB has changed, the pointer has changed too, but the