Updated xtrabackup to 2.2.7  seems like it helped a little bit. It now doesn't crash on every execution, however it still crashes with following error:

141216 11:23:05  innobackupex: Restarting xtrabackup with command: xtrabackup  --defaults-file="/mnt/backup/client_dbs_innodb/db29-slave/12-16-2014_10-55-34/backup-my.cnf"  --defaults-group="mysqld" --prepare --target-dir=/mnt/backup/client_dbs_innodb/db29-slave/12-16-2014_10-55-34 --use-memory=1G
for creating ib_logfile*

xtrabackup version 2.2.7 based on MySQL server 5.6.21 Linux (x86_64) (revision id: )
xtrabackup: cd to /mnt/backup/client_dbs_innodb/db29-slave/12-16-2014_10-55-34
xtrabackup: This target seems to be already prepared.
xtrabackup: notice: xtrabackup_logfile was already used to '--prepare'.
xtrabackup: using the following InnoDB configuration for recovery:
xtrabackup:   innodb_data_home_dir = ./
xtrabackup:   innodb_data_file_path = ibdata1:12M:autoextend
xtrabackup:   innodb_log_group_home_dir = ./
xtrabackup:   innodb_log_files_in_group = 2
xtrabackup:   innodb_log_file_size = 134217728
xtrabackup: using the following InnoDB configuration for recovery:
xtrabackup:   innodb_data_home_dir = ./
xtrabackup:   innodb_data_file_path = ibdata1:12M:autoextend
xtrabackup:   innodb_log_group_home_dir = ./
xtrabackup:   innodb_log_files_in_group = 2
xtrabackup:   innodb_log_file_size = 134217728
xtrabackup: Starting InnoDB instance for recovery.
xtrabackup: Using 1073741824 bytes for buffer pool (set by --use-memory parameter)
InnoDB: Using atomics to ref count buffer pool pages
InnoDB: The InnoDB memory heap is disabled
InnoDB: Mutexes and rw_locks use GCC atomic builtins
InnoDB: Memory barrier is not used
InnoDB: Compressed tables use zlib 1.2.3
InnoDB: Using CPU crc32 instructions
InnoDB: Initializing buffer pool, size = 1.0G
InnoDB: Completed initialization of buffer pool
InnoDB: Setting log file ./ib_logfile101 size to 128 MB
InnoDB: Progress in MB: 100
InnoDB: Setting log file ./ib_logfile1 size to 128 MB
InnoDB: Progress in MB: 100
InnoDB: Renaming log file ./ib_logfile101 to ./ib_logfile0
InnoDB: New log files created, LSN=487320310587
InnoDB: Highest supported file format is Barracuda.
InnoDB: 128 rollback segment(s) are active.
InnoDB: Waiting for purge to start
InnoDB: 5.6.21 started; log sequence number 487320310796

[notice (again)]
  If you use binary log and don't use any hack of group commit,
  the binary log position seems to be:
InnoDB: Last MySQL binlog file position 0 33456780, file name mysql-bin.001793

xtrabackup: starting shutdown with innodb_fast_shutdown = 1
10:23:21 UTC - xtrabackup got signal 11 ;
This could be because you hit a bug or data is corrupted.
This error can also be caused by malfunctioning hardware.
We will try our best to scrape up some info that will hopefully help
diagnose the problem, but since we have already crashed,
something is definitely wrong and this may fail.

Thread pointer: 0x0
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong...
stack_bottom = 0 thread_stack 0x10000
xtrabackup(my_print_stacktrace+0x35) [0x9f34bc]
xtrabackup(handle_fatal_signal+0x2bb) [0x7f66f3]
/lib64/libpthread.so.0() [0x300c40f710]

Please report a bug at https://bugs.launchpad.net/percona-xtrabackup
innobackupex: got a fatal error with the following stacktrace: at /usr/bin/innobackupex line 2645
        main::apply_log() called at /usr/bin/innobackupex line 1561
innobackupex: Error:
innobackupex: xtrabackup (2nd execution) failed at /usr/bin/innobackupex line 2645.