Merge mysql.com:/home/mydev/mysql-5.0-bug19815

into  mysql.com:/home/mydev/mysql-5.1-bug19815

mysql-test/r/lock_multi.result

@@ -50,3 +50,11 @@ Field	Type	Null	Key	Default	Extra
 a	int(11)	YES		NULL	
 unlock tables;
 drop table t1;
+CREATE DATABASE mysqltest_1;
+FLUSH TABLES WITH READ LOCK;
+ DROP DATABASE mysqltest_1;
+DROP DATABASE mysqltest_1;
+ERROR HY000: Can't execute the query because you have a conflicting read lock
+UNLOCK TABLES;
+DROP DATABASE mysqltest_1;
+ERROR HY000: Can't drop database 'mysqltest_1'; database doesn't exist

mysql-test/t/lock_multi.test

@@ -126,3 +126,38 @@ show columns from t1;
 connection locker;
 unlock tables;
 drop table t1;
+
+#
+# Bug#19815 - CREATE/RENAME/DROP DATABASE can deadlock on a global read lock
+#
+connect (con1,localhost,root,,);
+connect (con2,localhost,root,,);
+#
+connection con1;
+CREATE DATABASE mysqltest_1;
+FLUSH TABLES WITH READ LOCK;
+#
+# With bug in place: acquire LOCK_mysql_create_table and
+# wait in wait_if_global_read_lock().
+connection con2;
+send DROP DATABASE mysqltest_1;
+--sleep 1
+#
+# With bug in place: try to acquire LOCK_mysql_create_table...
+# When fixed: Reject dropping db because of the read lock.
+connection con1;
+--error ER_CANT_UPDATE_WITH_READLOCK
+DROP DATABASE mysqltest_1;
+UNLOCK TABLES;
+#
+connection con2;
+reap;
+#
+connection default;
+disconnect con1;
+disconnect con2;
+# This must have been dropped by connection 2 already,
+# which waited until the global read lock was released.
+--error ER_DB_DROP_EXISTS
+DROP DATABASE mysqltest_1;
+

sql/sql_db.cc

@@ -538,16 +538,27 @@ bool mysql_create_db(THD *thd, char *db, HA_CREATE_INFO *create_info,
     my_error(ER_DB_CREATE_EXISTS, MYF(0), db);
     DBUG_RETURN(-1);
   }
-  
-  VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
 
-  /* do not create database if another thread is holding read lock */
+  /*
+    Do not create database if another thread is holding read lock.
+    Wait for global read lock before acquiring LOCK_mysql_create_db.
+    After wait_if_global_read_lock() we have protection against another
+    global read lock. If we would acquire LOCK_mysql_create_db first,
+    another thread could step in and get the global read lock before we
+    reach wait_if_global_read_lock(). If this thread tries the same as we
+    (admin a db), it would then go and wait on LOCK_mysql_create_db...
+    Furthermore wait_if_global_read_lock() checks if the current thread
+    has the global read lock and refuses the operation with
+    ER_CANT_UPDATE_WITH_READLOCK if applicable.
+  */
   if (wait_if_global_read_lock(thd, 0, 1))
   {
     error= -1;
     goto exit2;
   }
 
+  VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
+
   /* Check directory */
   path_len= build_table_filename(path, sizeof(path), db, "", "");
   path[path_len-1]= 0;                    // Remove last '/' from path
@@ -655,9 +666,9 @@ bool mysql_create_db(THD *thd, char *db, HA_CREATE_INFO *create_info,
   }
 
 exit:
+  VOID(pthread_mutex_unlock(&LOCK_mysql_create_db));
   start_waiting_global_read_lock(thd);
 exit2:
-  VOID(pthread_mutex_unlock(&LOCK_mysql_create_db));
   DBUG_RETURN(error);
 }
 
@@ -671,12 +682,23 @@ bool mysql_alter_db(THD *thd, const char *db, HA_CREATE_INFO *create_info)
   int error= 0;
   DBUG_ENTER("mysql_alter_db");
 
-  VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
-
-  /* do not alter database if another thread is holding read lock */
+  /*
+    Do not alter database if another thread is holding read lock.
+    Wait for global read lock before acquiring LOCK_mysql_create_db.
+    After wait_if_global_read_lock() we have protection against another
+    global read lock. If we would acquire LOCK_mysql_create_db first,
+    another thread could step in and get the global read lock before we
+    reach wait_if_global_read_lock(). If this thread tries the same as we
+    (admin a db), it would then go and wait on LOCK_mysql_create_db...
+    Furthermore wait_if_global_read_lock() checks if the current thread
+    has the global read lock and refuses the operation with
+    ER_CANT_UPDATE_WITH_READLOCK if applicable.
+  */
   if ((error=wait_if_global_read_lock(thd,0,1)))
     goto exit2;
 
+  VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
+
   /* 
      Recreate db options file: /dbpath/.db.opt
      We pass MY_DB_OPT_FILE as "extension" to avoid
@@ -721,9 +743,9 @@ bool mysql_alter_db(THD *thd, const char *db, HA_CREATE_INFO *create_info)
   send_ok(thd, result);
 
 exit:
+  VOID(pthread_mutex_unlock(&LOCK_mysql_create_db));
   start_waiting_global_read_lock(thd);
 exit2:
-  VOID(pthread_mutex_unlock(&LOCK_mysql_create_db));
   DBUG_RETURN(error);
 }
 
@@ -755,15 +777,26 @@ bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
   TABLE_LIST* dropped_tables= 0;
   DBUG_ENTER("mysql_rm_db");
 
-  VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
-
-  /* do not drop database if another thread is holding read lock */
+  /*
+    Do not drop database if another thread is holding read lock.
+    Wait for global read lock before acquiring LOCK_mysql_create_db.
+    After wait_if_global_read_lock() we have protection against another
+    global read lock. If we would acquire LOCK_mysql_create_db first,
+    another thread could step in and get the global read lock before we
+    reach wait_if_global_read_lock(). If this thread tries the same as we
+    (admin a db), it would then go and wait on LOCK_mysql_create_db...
+    Furthermore wait_if_global_read_lock() checks if the current thread
+    has the global read lock and refuses the operation with
+    ER_CANT_UPDATE_WITH_READLOCK if applicable.
+  */
   if (wait_if_global_read_lock(thd, 0, 1))
   {
     error= -1;
     goto exit2;
   }
 
+  VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
+
   length= build_table_filename(path, sizeof(path), db, "", "");
   strmov(path+length, MY_DB_OPT_FILE);		// Append db option file name
   del_dbopt(path);				// Remove dboption hash entry
@@ -872,7 +905,6 @@ bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
 exit:
   (void)sp_drop_db_routines(thd, db); /* QQ Ignore errors for now  */
   (void)evex_drop_db_events(thd, db); /* QQ Ignore errors for now  */
-  start_waiting_global_read_lock(thd);
   /*
     If this database was the client's selected database, we silently change the
     client's selected database to nothing (to have an empty SELECT DATABASE()
@@ -901,9 +933,9 @@ bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
     thd->db= 0;
     thd->db_length= 0;
   }
-exit2:
   VOID(pthread_mutex_unlock(&LOCK_mysql_create_db));
-
+  start_waiting_global_read_lock(thd);
+exit2:
   DBUG_RETURN(error);
 }