Fix for bug #12704 "Server crashes during trigger execution".

This bug occurs when some trigger for table used by DML statement is created
or changed while statement was waiting in lock_tables(). In this situation
prelocking set which we have calculated becames invalid which can easily lead
to errors and even in some cases to crashes.

With proposed patch we no longer silently reopen tables in lock_tables(),
instead caller of lock_tables() becomes responsible for reopening tables and
recalculation of prelocking set.

sql/sp.cc

@@ -107,7 +107,7 @@ TABLE *open_proc_table_for_read(THD *thd, Open_tables_state *backup)
 {
   TABLE_LIST tables;
   TABLE *table;
-  bool refresh;
+  bool not_used;
   DBUG_ENTER("open_proc_table");
 
   /*
@@ -122,7 +122,7 @@ TABLE *open_proc_table_for_read(THD *thd, Open_tables_state *backup)
   bzero((char*) &tables, sizeof(tables));
   tables.db= (char*) "mysql";
   tables.table_name= tables.alias= (char*)"proc";
-  if (!(table= open_table(thd, &tables, thd->mem_root, &refresh,
+  if (!(table= open_table(thd, &tables, thd->mem_root, &not_used,
                           MYSQL_LOCK_IGNORE_FLUSH)))
   {
     thd->restore_backup_open_tables_state(backup);
@@ -138,7 +138,7 @@ TABLE *open_proc_table_for_read(THD *thd, Open_tables_state *backup)
     could lead to a deadlock if we have other tables opened.
   */
   if (!(thd->lock= mysql_lock_tables(thd, &table, 1,
-                                     MYSQL_LOCK_IGNORE_FLUSH)))
+                                     MYSQL_LOCK_IGNORE_FLUSH, &not_used)))
   {
     close_proc_table(thd, backup);
     DBUG_RETURN(0);
@@ -1265,7 +1265,8 @@ static bool add_used_routine(LEX *lex, Query_arena *arena,
 
 
 /*
-  Add routine to the set of stored routines used by statement.
+  Add routine which is explicitly used by statement to the set of stored
+  routines used by this statement.
 
   SYNOPSIS
     sp_add_used_routine()
@@ -1276,7 +1277,8 @@ static bool add_used_routine(LEX *lex, Query_arena *arena,
       rt_type - routine type (one of TYPE_ENUM_PROCEDURE/...)
 
   NOTES
-    Will also add element to end of 'LEX::sroutines_list' list.
+    Will also add element to end of 'LEX::sroutines_list' list (and will
+    take into account that this is explicitly used routine).
 
     To be friendly towards prepared statements one should pass
     persistent arena as second argument.
@@ -1287,6 +1289,37 @@ void sp_add_used_routine(LEX *lex, Query_arena *arena,
 {
   rt->set_routine_type(rt_type);
   (void)add_used_routine(lex, arena, &rt->m_sroutines_key);
+  lex->sroutines_list_own_last= lex->sroutines_list.next;
+  lex->sroutines_list_own_elements= lex->sroutines_list.elements;
+}
+
+
+/*
+  Remove routines which are only indirectly used by statement from
+  the set of routines used by this statement.
+
+  SYNOPSIS
+    sp_remove_not_own_routines()
+      lex  LEX representing statement
+*/
+
+void sp_remove_not_own_routines(LEX *lex)
+{
+  Sroutine_hash_entry *not_own_rt, *next_rt;
+  for (not_own_rt= *(Sroutine_hash_entry **)lex->sroutines_list_own_last;
+       not_own_rt; not_own_rt= next_rt)
+  {
+    /*
+      It is safe to obtain not_own_rt->next after calling hash_delete() now
+      but we want to be more future-proof.
+    */
+    next_rt= not_own_rt->next;
+    hash_delete(&lex->sroutines, (byte *)not_own_rt);
+  }
+
+  *(Sroutine_hash_entry **)lex->sroutines_list_own_last= NULL;
+  lex->sroutines_list.next= lex->sroutines_list_own_last;
+  lex->sroutines_list.elements= lex->sroutines_list_own_elements;
 }
 
 
@@ -1343,6 +1376,28 @@ static void sp_update_stmt_used_routines(THD *thd, LEX *lex, HASH *src)
 }
 
 
+/*
+  Add contents of list representing set of routines to the set of
+  routines used by statement.
+
+  SYNOPSIS
+    sp_update_stmt_used_routines()
+      thd  Thread context
+      lex  LEX representing statement
+      src  List representing set from which routines will be added
+
+  NOTE
+    It will also add elements to end of 'LEX::sroutines_list' list.
+*/
+
+static void sp_update_stmt_used_routines(THD *thd, LEX *lex, SQL_LIST *src)
+{
+  for (Sroutine_hash_entry *rt= (Sroutine_hash_entry *)src->first;
+       rt; rt= rt->next)
+    (void)add_used_routine(lex, thd->stmt_arena, &rt->key);
+}
+
+
 /*
   Cache sub-set of routines used by statement, add tables used by these
   routines to statement table list. Do the same for all routines used
@@ -1463,7 +1518,7 @@ sp_cache_routines_and_add_tables_for_view(THD *thd, LEX *lex, LEX *aux_lex)
 {
   Sroutine_hash_entry **last_cached_routine_ptr=
                           (Sroutine_hash_entry **)lex->sroutines_list.next;
-  sp_update_stmt_used_routines(thd, lex, &aux_lex->sroutines);
+  sp_update_stmt_used_routines(thd, lex, &aux_lex->sroutines_list);
   (void)sp_cache_routines_and_add_tables_aux(thd, lex, 
                                              *last_cached_routine_ptr, FALSE);
 }