Fixed Bug#11756013 (formerly known as bug#47870):

BOGUS "THE TABLE MYSQL.PROC IS MISSING,..."

There was a race condition between loading a stored routine
(function/procedure/trigger) specified by fully qualified name
SCHEMA_NAME.PROC_NAME and dropping the stored routine database.

The problem was that there is a window for race condition when one server
thread tries to load a stored routine being executed and the other thread
tries to drop the stored routine schema.

This condition race window exists in implementation of function
mysql_change_db() called by db_load_routine() during loading of stored
routine to cache. Function mysql_change_db() calls check_db_dir_existence()
that might failed because specified database was dropped during concurrent
execution of DROP SCHEMA statement. db_load_routine() calls mysql_change_db()
with flag 'force_switch' set to 'true' value so when referenced db is not found
then my_error() is not called and function mysql_change_db() returns ok.
This shadows information about schema opening error in db_load_routine().
Then db_load_routine() makes attempt to parse stored routine that is failed.
This makes to return error to sp_cache_routines_and_add_tables_aux() but since
during error generation a call to my_error wasn't made and hence
THD::main_da wasn't set we set the generic "mysql.proc table corrupt" error
when running sp_cache_routines_and_add_tables_aux().

The fix is to install an error handler inside db_load_routine() for
the mysql_op_change_db() call, and check later if the ER_BAD_DB_ERROR
was caught.


sql/sql_db.cc:
  Added synchronization point "before_db_dir_check" to emulate a race condition during
  processing of CALL/DROP SCHEMA.

1 files changed, 13 insertions, 1 deletions

diff --git a/mysql-test/r/sp_sync.result b/mysql-test/r/sp_sync.result
index afa37e70531..17292f4c1a8 100644
--- a/mysql-test/r/sp_sync.result
+++ b/mysql-test/r/sp_sync.result
@@ -1,4 +1,4 @@
-Tests of syncronization of stored procedure execution.
+Tests of synchronization of stored procedure execution.
 #
 # Bug#48157: crash in Item_field::used_tables
 #
@@ -20,4 +20,16 @@ SET DEBUG_SYNC = 'now SIGNAL go';
 # code, this test statement will hang.
 DROP TABLE t1, t2;
 DROP PROCEDURE p1;
+#
+# test for bug#11756013
+#
+DROP SCHEMA IF EXISTS s1;
+CREATE SCHEMA s1;
+CREATE PROCEDURE s1.p1() BEGIN END;
+SET DEBUG_SYNC='before_db_dir_check SIGNAL check_db WAIT_FOR dropped_schema';
+CALL s1.p1;
+SET DEBUG_SYNC='now WAIT_FOR check_db';
+DROP SCHEMA s1;
+SET DEBUG_SYNC='now SIGNAL dropped_schema';
+ERROR 42000: Unknown database 's1'
 SET DEBUG_SYNC = 'RESET';