xtrabackup hangs with xtrabackup_logfile growing

(Sorry, I posted this in the wrong forum section before.)

I’m trying to do a backup with the following command (which works fine with other servers):

/usr/bin/innobackupex --no-lock --safe-slave-backup --slave-info "/some/location"

So what this does is:

InnoDB Backup Utility v1.5.1-xtrabackup; Copyright 2003, 2009 Innobase Oy
and Percona LLC and/or its affiliates 2009-2013. All Rights Reserved.

This software is published under
the GNU GENERAL PUBLIC LICENSE Version 2, June 1991.

Get the latest version of Percona XtraBackup, documentation, and help resources:

141031 10:16:26 innobackupex: Connecting to MySQL server with DSN 'dbi:mysql:;mysql_read_default_file=/root/.my.cnf;mysql_read_default_group=xtrabackup' (using password: NO).
141031 10:16:26 innobackupex: Connected to MySQL server
141031 10:16:26 innobackupex: Executing a version check against the server...
141031 10:16:26 innobackupex: Done.
IMPORTANT: Please check that the backup run completes successfully.
At the end of a successful backup run innobackupex
prints "completed OK!".

innobackupex: Using mysql server version 5.5.40-36.1-log

innobackupex: Created backup directory /some/location/2014-10-31_10-16-27

141031 10:16:27 innobackupex: Starting ibbackup with command: xtrabackup --defaults-group="mysqld" --backup --suspend-at-end --target-dir=/some/location/2014-10-31_10-16-27 --tmpdir=/var/lib/mysql/tmp --extra-lsndir='/var/lib/mysql/tmp'
innobackupex: Waiting for ibbackup (pid=3501) to suspend
innobackupex: Suspend file '/some/location/2014-10-31_10-16-27/xtrabackup_suspended_2'

xtrabackup version 2.2.5 based on MySQL server 5.6.21 Linux (x86_64) (revision id: )
xtrabackup: uses posix_fadvise().
xtrabackup: cd to /var/lib/mysql/data
xtrabackup: open files limit requested 65535, set to 65535
xtrabackup: using the following InnoDB configuration:
xtrabackup: innodb_data_home_dir = ./
xtrabackup: innodb_data_file_path = ibdata1:100M:autoextend:max:100G
xtrabackup: innodb_log_group_home_dir = ./
xtrabackup: innodb_log_files_in_group = 2
xtrabackup: innodb_log_file_size = 3221225472
xtrabackup: using O_DIRECT

And it just hangs there forever. In the target directory, I see an ever-growing xtrabackup_logfile. I let it grow up to 20GB then I killed the backup.
Am I doing something wrong?

Update: I see no change if I remove the

--no-lock --safe-slave-backup --slave-info

options (or any subset of them).

Can you please share entire backup log ? How big is your transcation logs i.e. ib_logfile* ? Can you please share your my.cnf please.
I foresee your transaction logs are small in size and your server is loaded for writes during backup. Can you confirm if that is the case ?
I would suggest to try to backup during database server off peak time and try to use latest version of xtrabackup.