Backport into build-200906240007-5.1.34sp1

> ------------------------------------------------------------
> revno: 2852.2.3
> revision-id: davi.arnaut@sun.com-20090403194600-60ufn0tz1gx1kl0l
> parent: gni@mysql.com-20090403184200-vnjtpsv4an79w8bu
> parent: davi.arnaut@sun.com-20090403191154-0ho2nai3chjsmpof
> committer: Davi Arnaut <Davi.Arnaut@Sun.COM>
> branch nick: 43230-5.1
> timestamp: Fri 2009-04-03 16:46:00 -0300
> message:
>   Merge Bug#43230 into mysql-5.1-bugteam
>     ------------------------------------------------------------
>     revno: 1810.3855.16
>     revision-id: davi.arnaut@sun.com-20090403191154-0ho2nai3chjsmpof
>     parent: chad@mysql.com-20090402152928-3ld60a56h86njcpg
>     committer: Davi Arnaut <Davi.Arnaut@Sun.COM>
>     branch nick: 43230-5.0
>     timestamp: Fri 2009-04-03 16:11:54 -0300
>     message:
>       Bug#43230: SELECT ... FOR UPDATE can hang with FLUSH TABLES WITH READ LOCK indefinitely
>       
>       The problem is that a SELECT .. FOR UPDATE statement might open
>       a table and later wait for a impeding global read lock without
>       noticing whether it is holding a table that is being waited upon
>       the the flush phase of the process that took the global read
>       lock.
>       
>       The same problem also affected the following statements:
>       
>       LOCK TABLES .. WRITE
>       UPDATE .. SET (update and multi-table update)
>       TRUNCATE TABLE ..
>       LOAD DATA ..
>       
>       The solution is to make the above statements wait for a impending
>       global read lock before opening the tables. If there is no
>       impending global read lock, the statement raises a temporary
>       protection against global read locks and progresses smoothly
>       towards completion.
>       
>       Important notice: the patch does not try to address all possible
>       cases, only those which are common and can be fixed unintrusively
>       enough for 5.0.

mysql-test/r/lock_multi.result

@@ -96,6 +96,61 @@ 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;

mysql-test/t/lock_multi.test

@@ -317,6 +317,134 @@ 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 $show_statement= SHOW PROCESSLIST;
+let $field= State;
+let $condition= = 'Flushing tables';
+--source include/wait_show_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
 

sql/sql_lex.cc

@@ -348,6 +348,7 @@ 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

sql/sql_lex.h

@@ -1745,6 +1745,22 @@ typedef struct st_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;
+
   st_lex();
 
   virtual ~st_lex()

sql/sql_parse.cc

@@ -2200,7 +2200,14 @@ mysql_execute_command(THD *thd)
       res= check_access(thd,
                         lex->exchange ? SELECT_ACL | FILE_ACL : SELECT_ACL,
                         any_db, 0, 0, 0, 0);
-    if (!res)
+
+    if (res)
+      break;
+
+    if (!thd->locked_tables && 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:
@@ -3006,6 +3013,9 @@ end_with_restore_list:
     DBUG_ASSERT(first_table == all_tables && first_table != 0);
     if (update_precheck(thd, all_tables))
       break;
+    if (!thd->locked_tables &&
+        !(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);
     res= (up_result= mysql_update(thd, all_tables,
@@ -3032,6 +3042,15 @@ 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 &&
+        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
@@ -3229,7 +3248,8 @@ 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;
   case SQLCOM_DELETE:
@@ -3402,6 +3422,10 @@ end_with_restore_list:
     if (check_one_table_access(thd, privilege, all_tables))
       goto error;
 
+    if (!thd->locked_tables &&
+        !(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);
@@ -3472,6 +3496,9 @@ end_with_restore_list:
     if (check_table_access(thd, LOCK_TABLES_ACL | SELECT_ACL, all_tables,
                            UINT_MAX, FALSE))
       goto error;
+    if (lex->protect_against_global_read_lock &&
+        !(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
+      goto error;
     thd->in_lock_tables=1;
     thd->options|= OPTION_TABLE_LOCK;
 

sql/sql_yacc.yy

@@ -6538,6 +6538,7 @@ 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
           {
@@ -12182,8 +12183,12 @@ table_lock_list:
 table_lock:
           table_ident opt_table_alias lock_option
           {
-            if (!Select->add_table_to_list(YYTHD, $1, $2, 0, (thr_lock_type) $3))
+            thr_lock_type lock_type= (thr_lock_type) $3;
+            if (!Select->add_table_to_list(YYTHD, $1, $2, 0, lock_type))
               MYSQL_YYABORT;
+            /* If table is to be write locked, protect from a impending GRL. */
+            if (lock_type >= TL_WRITE_ALLOW_WRITE)
+              Lex->protect_against_global_read_lock= TRUE;
           }
         ;