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, 41 insertions, 1 deletions

diff --git a/sql/sp.cc b/sql/sp.cc
index ddddaee2e10..78d1dc7e22c 100644
--- a/sql/sp.cc
+++ b/sql/sp.cc
@@ -708,6 +708,37 @@ Silence_deprecated_warning::handle_error(uint sql_errno, const char *message,
 }
 
 
+class Bad_db_error_handler : public Internal_error_handler
+{
+public:
+  Bad_db_error_handler()
+    :m_error_caught(false)
+  {}
+
+  virtual bool handle_error(uint sql_errno, const char *message,
+                            MYSQL_ERROR::enum_warning_level level,
+                            THD *thd);
+
+  bool error_caught() const { return m_error_caught; }
+
+private:
+  bool m_error_caught;
+};
+
+bool
+Bad_db_error_handler::handle_error(uint sql_errno, const char *message,
+                                   MYSQL_ERROR::enum_warning_level level,
+                                   THD *thd)
+{
+  if (sql_errno == ER_BAD_DB_ERROR)
+  {
+    m_error_caught= true;
+    return true;
+  }
+  return false;
+}
+
+
 static int
 db_load_routine(THD *thd, int type, sp_name *name, sp_head **sphp,
                 ulong sql_mode, const char *params, const char *returns,
@@ -725,7 +756,7 @@ db_load_routine(THD *thd, int type, sp_name *name, sp_head **sphp,
   ha_rows old_select_limit= thd->variables.select_limit;
   sp_rcontext *old_spcont= thd->spcont;
   Silence_deprecated_warning warning_handler;
-
+  Bad_db_error_handler db_not_exists_handler;
   char definer_user_name_holder[USERNAME_LENGTH + 1];
   LEX_STRING definer_user_name= { definer_user_name_holder,
                                   USERNAME_LENGTH };
@@ -766,6 +797,7 @@ db_load_routine(THD *thd, int type, sp_name *name, sp_head **sphp,
     goto end;
   }
 
+  thd->push_internal_handler(&db_not_exists_handler);
   /*
     Change the current database (if needed).
 
@@ -776,9 +808,17 @@ db_load_routine(THD *thd, int type, sp_name *name, sp_head **sphp,
                           &cur_db_changed))
   {
     ret= SP_INTERNAL_ERROR;
+    thd->pop_internal_handler();
     goto end;
   }
+  thd->pop_internal_handler();
+  if (db_not_exists_handler.error_caught())
+  {
+    ret= SP_INTERNAL_ERROR;
+    my_error(ER_BAD_DB_ERROR, MYF(0), name->m_db.str);
 
+    goto end;
+  }
   thd->spcont= NULL;
 
   {