Bug #11764779 (former 57649)

FLUSH TABLES under FLUSH TABLES <list> WITH READ LOCK leads 
to assert failure.

This assert was triggered if a statement tried up upgrade a metadata
lock with an active FLUSH TABLE <list> WITH READ LOCK. The assert 
checks that the connection already holds a global intention exclusive
metadata lock. However, FLUSH TABLE <list> WITH READ LOCK does not
acquire this lock in order to be compatible with FLUSH TABLES WITH
READ LOCK. Therefore any metadata lock upgrade caused the assert to
be triggered.

This patch fixes the problem by preventing metadata lock upgrade
if the connection has an active FLUSH TABLE <list> WITH READ LOCK.
ER_TABLE_NOT_LOCKED_FOR_WRITE will instead be reported to the client.

Test case added to flush.test.

6 files changed, 56 insertions, 30 deletions

diff --git a/sql/sql_base.cc b/sql/sql_base.cc
index 8b6cc2caf10..7c020515f87 100644
--- a/sql/sql_base.cc
+++ b/sql/sql_base.cc
@@ -1026,7 +1026,7 @@ bool close_cached_tables(THD *thd, TABLE_LIST *tables,
          table_list= table_list->next_global)
     {
       /* A check that the table was locked for write is done by the caller. */
-      TABLE *table= find_table_for_mdl_upgrade(thd->open_tables, table_list->db,
+      TABLE *table= find_table_for_mdl_upgrade(thd, table_list->db,
                                                table_list->table_name, TRUE);
 
       /* May return NULL if this table has already been closed via an alias. */
@@ -3120,22 +3120,26 @@ TABLE *find_locked_table(TABLE *list, const char *db, const char *table_name)
    lock from the list of open tables, emit error if no such table
    found.
 
-   @param list       List of TABLE objects to be searched
+   @param thd        Thread context
    @param db         Database name.
    @param table_name Name of table.
    @param no_error   Don't emit error if no suitable TABLE
                      instance were found.
 
+   @note This function checks if the connection holds a global IX
+         metadata lock. If no such lock is found, it is not safe to
+         upgrade the lock and ER_TABLE_NOT_LOCKED_FOR_WRITE will be
+         reported.
+
    @return Pointer to TABLE instance with MDL_SHARED_NO_WRITE,
            MDL_SHARED_NO_READ_WRITE, or MDL_EXCLUSIVE metadata
            lock, NULL otherwise.
 */
 
-TABLE *find_table_for_mdl_upgrade(TABLE *list, const char *db,
-                                  const char *table_name,
-                                  bool no_error)
+TABLE *find_table_for_mdl_upgrade(THD *thd, const char *db,
+                                  const char *table_name, bool no_error)
 {
-  TABLE *tab= find_locked_table(list, db, table_name);
+  TABLE *tab= find_locked_table(thd->open_tables, db, table_name);
 
   if (!tab)
   {
@@ -3143,19 +3147,29 @@ TABLE *find_table_for_mdl_upgrade(TABLE *list, const char *db,
       my_error(ER_TABLE_NOT_LOCKED, MYF(0), table_name);
     return NULL;
   }
-  else
+
+  /*
+    It is not safe to upgrade the metadata lock without a global IX lock.
+    This can happen with FLUSH TABLES <list> WITH READ LOCK as we in these
+    cases don't take a global IX lock in order to be compatible with
+    global read lock.
+  */
+  if (!thd->mdl_context.is_lock_owner(MDL_key::GLOBAL, "", "",
+                                      MDL_INTENTION_EXCLUSIVE))
   {
-    while (tab->mdl_ticket != NULL &&
-           !tab->mdl_ticket->is_upgradable_or_exclusive() &&
-           (tab= find_locked_table(tab->next, db, table_name)))
-      continue;
-    if (!tab)
-    {
-      if (!no_error)
-        my_error(ER_TABLE_NOT_LOCKED_FOR_WRITE, MYF(0), table_name);
-      return 0;
-    }
+    if (!no_error)
+      my_error(ER_TABLE_NOT_LOCKED_FOR_WRITE, MYF(0), table_name);
+    return NULL;
   }
+
+  while (tab->mdl_ticket != NULL &&
+         !tab->mdl_ticket->is_upgradable_or_exclusive() &&
+         (tab= find_locked_table(tab->next, db, table_name)))
+    continue;
+
+  if (!tab && !no_error)
+    my_error(ER_TABLE_NOT_LOCKED_FOR_WRITE, MYF(0), table_name);
+
   return tab;
 }
 
@@ -4653,8 +4667,7 @@ open_tables_check_upgradable_mdl(THD *thd, TABLE_LIST *tables_start,
         Note that find_table_for_mdl_upgrade() will report an error if
         no suitable ticket is found.
       */
-      if (!find_table_for_mdl_upgrade(thd->open_tables, table->db,
-                                      table->table_name, FALSE))
+      if (!find_table_for_mdl_upgrade(thd, table->db, table->table_name, false))
         return TRUE;
     }
   }
diff --git a/sql/sql_base.h b/sql/sql_base.h
index 35fa04b3674..dc8320687fc 100644
--- a/sql/sql_base.h
+++ b/sql/sql_base.h
@@ -1,4 +1,4 @@
-/* Copyright 2006-2008 MySQL AB, 2008-2009 Sun Microsystems, Inc.
+/* Copyright (c) 2006, 2011, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -290,7 +290,7 @@ bool tdc_open_view(THD *thd, TABLE_LIST *table_list, const char *alias,
                    char *cache_key, uint cache_key_length,
                    MEM_ROOT *mem_root, uint flags);
 void tdc_flush_unused_tables();
-TABLE *find_table_for_mdl_upgrade(TABLE *list, const char *db,
+TABLE *find_table_for_mdl_upgrade(THD *thd, const char *db,
                                   const char *table_name,
                                   bool no_error);
 void mark_tmp_table_for_reuse(TABLE *table);
diff --git a/sql/sql_reload.cc b/sql/sql_reload.cc
index 0810459cb49..a09aa5511bd 100644
--- a/sql/sql_reload.cc
+++ b/sql/sql_reload.cc
@@ -1,4 +1,4 @@
-/* Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -220,12 +220,26 @@ bool reload_acl_and_cache(THD *thd, unsigned long options,
         if (tables)
         {
           for (TABLE_LIST *t= tables; t; t= t->next_local)
-            if (!find_table_for_mdl_upgrade(thd->open_tables, t->db,
-                                            t->table_name, FALSE))
+            if (!find_table_for_mdl_upgrade(thd, t->db, t->table_name, false))
               return 1;
         }
         else
         {
+          /*
+            It is not safe to upgrade the metadata lock without GLOBAL IX lock.
+            This can happen with FLUSH TABLES <list> WITH READ LOCK as we in these
+            cases don't take a GLOBAL IX lock in order to be compatible with
+            global read lock.
+          */
+          if (thd->open_tables &&
+              !thd->mdl_context.is_lock_owner(MDL_key::GLOBAL, "", "",
+                                              MDL_INTENTION_EXCLUSIVE))
+          {
+            my_error(ER_TABLE_NOT_LOCKED_FOR_WRITE, MYF(0),
+                     thd->open_tables->s->table_name.str);
+            return true;
+          }
+
           for (TABLE *tab= thd->open_tables; tab; tab= tab->next)
           {
             if (! tab->mdl_ticket->is_upgradable_or_exclusive())
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index 2855bb0ec4a..677d2095a77 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -1917,7 +1917,7 @@ bool mysql_rm_table(THD *thd,TABLE_LIST *tables, my_bool if_exists,
             by parser) it is safe to cache pointer to the TABLE instances
             in its elements.
           */
-          table->table= find_table_for_mdl_upgrade(thd->open_tables, table->db,
+          table->table= find_table_for_mdl_upgrade(thd, table->db,
                                                    table->table_name, false);
           if (!table->table)
             DBUG_RETURN(true);
diff --git a/sql/sql_trigger.cc b/sql/sql_trigger.cc
index c2e3cd9944a..e986f6d7e92 100644
--- a/sql/sql_trigger.cc
+++ b/sql/sql_trigger.cc
@@ -1,4 +1,4 @@
-/* Copyright (C) 2004-2005 MySQL AB, 2008-2009 Sun Microsystems, Inc
+/* Copyright (c) 2004, 2011, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -467,8 +467,7 @@ bool mysql_create_or_drop_trigger(THD *thd, TABLE_LIST *tables, bool create)
   if (thd->locked_tables_mode)
   {
     /* Under LOCK TABLES we must only accept write locked tables. */
-    if (!(tables->table= find_table_for_mdl_upgrade(thd->open_tables,
-                                                    tables->db,
+    if (!(tables->table= find_table_for_mdl_upgrade(thd, tables->db,
                                                     tables->table_name,
                                                     FALSE)))
       goto end;
diff --git a/sql/sql_truncate.cc b/sql/sql_truncate.cc
index 909c6a08b67..67ed608f114 100644
--- a/sql/sql_truncate.cc
+++ b/sql/sql_truncate.cc
@@ -1,4 +1,4 @@
-/* Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -327,7 +327,7 @@ bool Truncate_statement::lock_table(THD *thd, TABLE_LIST *table_ref,
   */
   if (thd->locked_tables_mode)
   {
-    if (!(table= find_table_for_mdl_upgrade(thd->open_tables, table_ref->db,
+    if (!(table= find_table_for_mdl_upgrade(thd, table_ref->db,
                                             table_ref->table_name, FALSE)))
       DBUG_RETURN(TRUE);