database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-08-01 03:47:19 +03:00
Code Activity

Bug#19815 - CREATE/RENAME/DROP DATABASE can deadlock on a global read lock

Browse Source 
The order of acquiring LOCK_mysql_create_db
and wait_if_global_read_lock() was wrong. It could happen
that a thread held LOCK_mysql_create_db while waiting for
the global read lock to be released. The thread with the
global read lock could try to administrate a database too.
It would first try to lock LOCK_mysql_create_db and hang...

The check if the current thread has the global read lock
is done in wait_if_global_read_lock(), which could not be
reached because of the hang in LOCK_mysql_create_db.

Now I exchanged the order of acquiring LOCK_mysql_create_db
and wait_if_global_read_lock(). This makes 
wait_if_global_read_lock() fail with an error message for
the thread with the global read lock. No deadlock happens.
This commit is contained in:
ingo@mysql.com
2006-05-29 15:26:23 +02:00
parent da1fdb8a5f
commit d00441e328
3 changed files with 89 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files

60
sql/sql_db.cc
View File

@ -424,16 +424,27 @@ 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 */
strxmov(path, mysql_data_home, "/", db, NullS);
path_len= unpack_dirname(path,path); // Convert if not unix
@ -537,9 +548,9 @@ 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);
}
@ -553,12 +564,23 @@ 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));
/* Check directory */
strxmov(path, mysql_data_home, "/", db, "/", MY_DB_OPT_FILE, NullS);
fn_format(path, path, "", "", MYF(MY_UNPACK_FILENAME));
@ -596,9 +618,9 @@ 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);
}
@ -630,15 +652,26 @@ 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));
(void) sprintf(path,"%s/%s",mysql_data_home,db);
length= unpack_dirname(path,path); // Convert if not unix
strmov(path+length, MY_DB_OPT_FILE); // Append db option file name
@ -747,7 +780,6 @@ 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 */
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()
@ -776,9 +808,9 @@ 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);
}