Backport of:

------------------------------------------------------------
revno: 2476.1116.1
committer: davi@mysql.com/endora.local
timestamp: Fri 2007-12-14 10:10:19 -0200
message:
DROP TABLE under LOCK TABLES simultaneous to a FLUSH TABLES
WITH READ LOCK (global read lock) can lead to a deadlock.

The solution is to not wait for the global read lock if the
thread is holding any locked tables.

Related to bugs 23713 and 32395. This issues is being fixed
only on 6.0 because it depends on the fix for bug 25858 --
which was fixed only on 6.0.

mysql-test/r/lock_multi.result

@@ -210,3 +210,12 @@ select @tlwa < @tlwb;
 @tlwa < @tlwb
 1
 End of 5.1 tests
+drop table if exists t1;
+create table t1 (i int);
+connection: default
+lock tables t1 write;
+connection: flush
+flush tables with read lock;;
+connection: default
+flush tables;
+drop table t1;

mysql-test/t/lock_multi.test

@@ -636,6 +636,41 @@ select @tlwa < @tlwb;
 
 --echo End of 5.1 tests
 
+#
+# Test that DROP TABLES does not wait for a impending FLUSH TABLES
+# WITH READ LOCK
+#
+
+--disable_warnings
+drop table if exists t1;
+--enable_warnings
+create table t1 (i int);
+connect (flush,localhost,root,,test,,);
+connection default;
+--echo connection: default
+lock tables t1 write;
+connection flush;
+--echo connection: flush
+--send flush tables with read lock;
+connection default;
+--echo connection: default
+let $wait_condition=
+  select count(*) = 1 from information_schema.processlist
+  where state = "Flushing tables";
+--source include/wait_condition.inc
+flush tables;
+let $wait_condition=
+  select count(*) = 1 from information_schema.processlist
+  where state = "Flushing tables";
+--source include/wait_condition.inc
+drop table t1;
+let $wait_condition=
+  select count(*) = 0 from information_schema.processlist
+  where state = "Flushing tables";
+--source include/wait_condition.inc
+connection flush;
+--reap
+connection default;
+disconnect flush;
 # Wait till all disconnects are completed
 --source include/wait_until_count_sessions.inc
-

sql/sql_table.cc

@@ -1766,7 +1766,8 @@ void write_bin_log(THD *thd, bool clear_error,
     If a table is in use, we will wait for all users to free the table
     before dropping it
 
-    Wait if global_read_lock (FLUSH TABLES WITH READ LOCK) is set.
+    Wait if global_read_lock (FLUSH TABLES WITH READ LOCK) is set, but
+    not if under LOCK TABLES.
 
   RETURN
     FALSE OK.  In this case ok packet is sent to user
@@ -1777,7 +1778,7 @@ void write_bin_log(THD *thd, bool clear_error,
 bool mysql_rm_table(THD *thd,TABLE_LIST *tables, my_bool if_exists,
                     my_bool drop_temporary)
 {
-  bool error= FALSE, need_start_waiters= FALSE;
+  bool error= FALSE, need_start_waiting= FALSE;
   Drop_table_error_handler err_handler(thd->get_internal_handler());
   DBUG_ENTER("mysql_rm_table");
 
@@ -1785,14 +1786,10 @@ bool mysql_rm_table(THD *thd,TABLE_LIST *tables, my_bool if_exists,
 
   if (!drop_temporary)
   {
-    if ((error= wait_if_global_read_lock(thd, 0, 1)))
+    if (!thd->locked_tables &&
-    {
+        !(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
-      my_error(ER_TABLE_NOT_LOCKED_FOR_WRITE, MYF(0), tables->table_name);
       DBUG_RETURN(TRUE);
   }
-    else
-      need_start_waiters= TRUE;
-  }
 
   /*
     Acquire LOCK_open after wait_if_global_read_lock(). If we would hold
@@ -1804,7 +1801,7 @@ bool mysql_rm_table(THD *thd,TABLE_LIST *tables, my_bool if_exists,
   thd->pop_internal_handler();
 
 
-  if (need_start_waiters)
+  if (need_start_waiting)
     start_waiting_global_read_lock(thd);
 
   if (error)