diff --git a/mysql-test/r/lock_multi.result b/mysql-test/r/lock_multi.result index 1ab51e9fad5..debdf636eae 100644 --- a/mysql-test/r/lock_multi.result +++ b/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 diff --git a/mysql-test/t/lock_multi.test b/mysql-test/t/lock_multi.test index 3d07ec98d69..b963c217faa 100644 --- a/mysql-test/t/lock_multi.test +++ b/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; + diff --git a/sql/sql_db.cc b/sql/sql_db.cc index 3d035359b6f..94b389f9c93 100644 --- a/sql/sql_db.cc +++ b/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 @@ exit: 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); }