bzr commit into mysql-6.0-bugteam branch (davi:3179) Bug#43230

[Davi Arnaut]

# At a local mysql-6.0-bugteam repository of davi

 3179 Davi Arnaut	2009-04-03 [merge]
      Merge Bug#43230 into mysql-6.0-bugteam

    modified:
      mysql-test/r/lock_multi.result
      mysql-test/t/lock_multi.test
      sql/sql_lex.cc
      sql/sql_lex.h
      sql/sql_parse.cc
      sql/sql_yacc.yy
=== modified file 'mysql-test/r/lock_multi.result'
--- a/mysql-test/r/lock_multi.result	2009-03-24 14:24:44 +0000
+++ b/mysql-test/r/lock_multi.result	2009-04-03 21:07:07 +0000
@@ -97,6 +97,61 @@ alter table t1 auto_increment=0;
 alter table t1 auto_increment=0;
 unlock tables;
 drop table t1;
+create table t1 (a int);
+create table t2 like t1;
+# con1
+lock tables t1 write;
+# con2
+flush tables with read lock;
+# con5
+# global read lock is taken
+# con3
+select * from t2 for update;
+# waiting for release of read lock
+# con4
+# would hang and later cause a deadlock
+flush tables t2;
+# clean up
+unlock tables;
+unlock tables;
+a
+drop table t1,t2;
+#
+# Lightweight version:
+# Ensure that the wait for a GRL is done before opening tables.
+#
+create table t1 (a int);
+create table t2 like t1;
+#
+# UPDATE
+#
+# default
+flush tables with read lock;
+# con1
+update t2 set a = 1;
+# default
+# statement is waiting for release of read lock
+# con2
+flush table t2;
+# default
+unlock tables;
+# con1
+#
+# LOCK TABLES .. WRITE
+#
+# default
+flush tables with read lock;
+# con1
+lock tables t2 write;
+# default
+# statement is waiting for release of read lock
+# con2
+flush table t2;
+# default
+unlock tables;
+# con1
+unlock tables;
+drop table t1,t2;
 End of 5.0 tests
 create table t1 (i int);
 lock table t1 read;

=== modified file 'mysql-test/t/lock_multi.test'
--- a/mysql-test/t/lock_multi.test	2009-03-24 14:24:44 +0000
+++ b/mysql-test/t/lock_multi.test	2009-04-03 21:07:07 +0000
@@ -318,6 +318,134 @@ reap;
 connection locker;
 drop table t1;
 
+#
+# Bug#43230: SELECT ... FOR UPDATE can hang with FLUSH TABLES WITH READ LOCK indefinitely
+#
+
+connect (con1,localhost,root,,);
+connect (con2,localhost,root,,);
+connect (con3,localhost,root,,);
+connect (con4,localhost,root,,);
+connect (con5,localhost,root,,);
+
+create table t1 (a int);
+create table t2 like t1;
+
+connection con1;
+--echo # con1
+lock tables t1 write;
+connection con2;
+--echo # con2
+send flush tables with read lock;
+connection con5;
+--echo # con5
+let $wait_condition=
+  select count(*) = 1 from information_schema.processlist
+  where state = "Waiting for table" and info = "flush tables with read lock";
+--source include/wait_condition.inc
+--echo # global read lock is taken
+connection con3;
+--echo # con3
+send select * from t2 for update;
+connection con5;
+let $show_statement= SHOW PROCESSLIST;
+let $field= State;
+let $condition= = 'Waiting for release of readlock';
+--source include/wait_show_condition.inc
+--echo # waiting for release of read lock
+connection con4;
+--echo # con4
+--echo # would hang and later cause a deadlock
+flush tables t2;
+connection con1;
+--echo # clean up
+unlock tables;
+connection con2;
+--reap
+unlock tables;
+connection con3;
+--reap
+connection default;
+disconnect con5;
+disconnect con4;
+disconnect con3;
+disconnect con2;
+disconnect con1;
+
+drop table t1,t2;
+
+--echo #
+--echo # Lightweight version:
+--echo # Ensure that the wait for a GRL is done before opening tables.
+--echo #
+
+connect (con1,localhost,root,,);
+connect (con2,localhost,root,,);
+
+create table t1 (a int);
+create table t2 like t1;
+
+--echo #
+--echo # UPDATE
+--echo #
+
+connection default;
+--echo # default
+flush tables with read lock;
+connection con1;
+--echo # con1
+send update t2 set a = 1;
+connection default;
+--echo # default
+let $show_statement= SHOW PROCESSLIST;
+let $field= State;
+let $condition= = 'Waiting for release of readlock';
+--source include/wait_show_condition.inc
+--echo # statement is waiting for release of read lock
+connection con2;
+--echo # con2
+flush table t2;
+connection default;
+--echo # default
+unlock tables;
+connection con1;
+--echo # con1
+--reap
+
+--echo #
+--echo # LOCK TABLES .. WRITE
+--echo #
+
+connection default;
+--echo # default
+flush tables with read lock;
+connection con1;
+--echo # con1
+send lock tables t2 write;
+connection default;
+--echo # default
+let $show_statement= SHOW PROCESSLIST;
+let $field= State;
+let $condition= = 'Waiting for release of readlock';
+--source include/wait_show_condition.inc
+--echo # statement is waiting for release of read lock
+connection con2;
+--echo # con2
+flush table t2;
+connection default;
+--echo # default
+unlock tables;
+connection con1;
+--echo # con1
+--reap
+unlock tables;
+
+connection default;
+disconnect con2;
+disconnect con1;
+
+drop table t1,t2;
+
 
 --echo End of 5.0 tests
 

=== modified file 'sql/sql_lex.cc'
--- a/sql/sql_lex.cc	2009-04-01 09:34:34 +0000
+++ b/sql/sql_lex.cc	2009-04-03 21:07:07 +0000
@@ -360,6 +360,7 @@ void lex_start(THD *thd)
   lex->nest_level=0 ;
   lex->allow_sum_func= 0;
   lex->in_sum_func= NULL;
+  lex->protect_against_global_read_lock= FALSE;
   /*
     ok, there must be a better solution for this, long-term
     I tried "bzero" in the sql_yacc.yy code, but that for

=== modified file 'sql/sql_lex.h'
--- a/sql/sql_lex.h	2009-03-19 16:42:23 +0000
+++ b/sql/sql_lex.h	2009-04-03 21:07:07 +0000
@@ -1839,6 +1839,22 @@ struct LEX: public Query_tables_list
   bool escape_used;
   bool is_lex_started; /* If lex_start() did run. For debugging. */
 
+  /*
+    Special case for SELECT .. FOR UPDATE and LOCK TABLES .. WRITE.
+
+    Protect from a impending GRL as otherwise the thread might deadlock
+    if it starts waiting for the GRL in mysql_lock_tables.
+
+    The protection is needed because there is a race between setting
+    the global read lock and waiting for all open tables to be closed.
+    The problem is a circular wait where a thread holding "old" open
+    tables will wait for the global read lock to be released while the
+    thread holding the global read lock will wait for all "old" open
+    tables to be closed -- the flush part of flush tables with read
+    lock.
+  */
+  bool protect_against_global_read_lock;
+
   LEX();
 
   virtual ~LEX()

=== modified file 'sql/sql_parse.cc'
--- a/sql/sql_parse.cc	2009-04-01 09:34:34 +0000
+++ b/sql/sql_parse.cc	2009-04-03 21:07:07 +0000
@@ -2152,8 +2152,15 @@ mysql_execute_command(THD *thd)
       res= check_access(thd,
                         privileges_requested,
                         any_db, 0, 0, 0, 0);
-    if (!res)
-      res= execute_sqlcom_select(thd, all_tables);
+
+    if (res)
+      break;
+
+    if (!thd->locked_tables_mode && lex->protect_against_global_read_lock &&
+        !(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
+      break;
+
+    res= execute_sqlcom_select(thd, all_tables);
     break;
   }
   case SQLCOM_PREPARE:
@@ -3110,6 +3117,9 @@ end_with_restore_list:
     DBUG_ASSERT(first_table == all_tables && first_table != 0);
     if (update_precheck(thd, all_tables))
       break;
+    if (!thd->locked_tables_mode &&
+        !(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
+      goto error;
     DBUG_ASSERT(select_lex->offset_limit == 0);
     unit->set_limit(select_lex);
     MYSQL_UPDATE_START(thd->query);
@@ -3137,6 +3147,15 @@ end_with_restore_list:
     else
       res= 0;
 
+    /*
+      Protection might have already been risen if its a fall through
+      from the SQLCOM_UPDATE case above.
+    */
+    if (!thd->locked_tables_mode &&
+        lex->sql_command == SQLCOM_UPDATE_MULTI &&
+        !(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
+      goto error;
+
     res= mysql_multi_update_prepare(thd);
 
 #ifdef HAVE_REPLICATION
@@ -3333,7 +3352,8 @@ end_with_restore_list:
                  ER(ER_LOCK_OR_ACTIVE_TRANSACTION), MYF(0));
       goto error;
     }
-
+    if (!(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
+      goto error;
     res= mysql_truncate(thd, first_table, 0);
 
     break;
@@ -3504,6 +3524,10 @@ end_with_restore_list:
     if (check_one_table_access(thd, privilege, all_tables))
       goto error;
 
+    if (!thd->locked_tables_mode &&
+        !(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
+      goto error;
+
     res= mysql_load(thd, lex->exchange, first_table, lex->field_list,
                     lex->update_list, lex->value_list, lex->duplicates,
                     lex->ignore, (bool) lex->local_file);
@@ -3615,6 +3639,9 @@ end_with_restore_list:
       goto error;
     /* release transactional metadata locks. */
     thd->mdl_context.release_all_locks();
+    if (lex->protect_against_global_read_lock &&
+        !(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
+      goto error;
 
     alloc_mdl_requests(all_tables, thd->locked_tables_list.locked_tables_root());
 

=== modified file 'sql/sql_yacc.yy'
--- a/sql/sql_yacc.yy	2009-03-18 21:09:40 +0000
+++ b/sql/sql_yacc.yy	2009-04-03 21:07:07 +0000
@@ -7175,6 +7175,7 @@ select_lock_type:
             lex->current_select->set_lock_for_tables(TL_WRITE);
             lex->current_select->lock_option= TL_WRITE;
             lex->safe_to_cache_query=0;
+            lex->protect_against_global_read_lock= TRUE;
           }
         | LOCK_SYM IN_SYM SHARE_SYM MODE_SYM
           {
@@ -12961,6 +12962,9 @@ table_lock:
           /* Compute the resulting lock method for all tables. */
           if (!$3.lock_transactional)
             Lex->lock_transactional= FALSE;
+          /* If table is to be write locked, protect from a impending GRL. */
+          if ($3.lock_type >= TL_WRITE_ALLOW_WRITE)
+            Lex->protect_against_global_read_lock= TRUE;
         }
         ;
 


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