6.4.1 still getting lockups

Gone down again today at around 19:48 - after around 2 days of uptime (this is obviously unacceptable)

I left a series of monitoring tasks running - the last output from "vmstat" was

procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
3 1 32 42520 428 294876 0 0 2028 4042 2423 2309 7 56 16 21
1 0 32 38780 428 297496 0 0 1280 33166 6088 2390 5 77 0 18
1 0 32 39248 428 297524 0 0 1056 30667 2413 1977 2 59 25 14

Top memory usage (ps aux --sort -rss):

USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
mysql 3451 0.2 5.8 326748 29992 ? Sl Dec18 8:13 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib/mysql/plugin --user=mysql --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/run/mysqld/mysqld.sock --port=3306
root 3292 1.1 5.3 190700 26992 ? S<sl Dec18 41:53 /usr/sbin/readynasd -v 3 -t
media 2864 0.2 1.9 58856 9924 ? Ssl Dec18 9:54 /usr/sbin/forked-daapd -f
admin 3969 0.0 1.2 15272 6216 ? S Dec18 0:43 /usr/sbin/apache2 -k start
admin 4088 0.0 1.1 15020 6036 ? S Dec18 0:44 /usr/sbin/apache2 -k start
mike 5435 0.0 1.1 30616 6004 ? S Dec18 3:18 /usr/sbin/smbd
admin 19293 0.0 1.1 15004 5984 ? S Dec19 0:25 /usr/sbin/apache2 -k start
admin 3970 0.0 1.1 15056 5980 ? S Dec18 0:43 /usr/sbin/apache2 -k start
admin 8509 0.0 1.1 15068 5980 ? S Dec19 0:30 /usr/sbin/apache2 -k start

(i've now removed mysql completely - but according to the vmstat - theres still plenty of free memory)

Top CPU usage (ps aux --sort -pcpu) :  

USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
guest 16965 22.7 0.9 30040 5016 ? R 19:27 4:50 /usr/sbin/smbd
root 1590 22.0 0.0 0 0 ? S Dec18 782:18 [md126_raid5]
root 1564 20.4 0.0 0 0 ? S Dec18 727:00 [md127_raid5]
root 1471 7.7 0.0 0 0 ? S< Dec18 276:02 [kworker/0:1H]
root 3 3.4 0.0 0 0 ? S Dec18 123:58 [ksoftirqd/0]
root 17219 2.6 0.0 0 0 ? S 19:45 0:06 [kworker/u2:1]
root 16867 1.3 0.0 0 0 ? S 19:20 0:23 [kworker/u2:6]
root 16951 1.3 0.0 0 0 ? S 19:26 0:18 [kworker/u2:0]
root 16992 1.3 0.0 0 0 ? S 19:28 0:16 [kworker/u2:4]

And the last ps -ef it ran before locking up : 

------------------
Sun Dec 20 19:48:52 GMT 2015
------------------
UID PID PPID C STIME TTY TIME CMD
root 1 0 0 Dec18 ? 00:00:06 /sbin/init
root 2 0 0 Dec18 ? 00:00:00 [kthreadd]
root 3 2 3 Dec18 ? 02:03:58 [ksoftirqd/0]
root 5 2 0 Dec18 ? 00:00:00 [kworker/0:0H]
root 7 2 0 Dec18 ? 00:03:53 [rcu_sched]
root 8 2 0 Dec18 ? 00:00:00 [rcu_bh]
root 9 2 0 Dec18 ? 00:00:00 [migration/0]
root 10 2 0 Dec18 ? 00:00:00 [khelper]
root 11 2 0 Dec18 ? 00:00:00 [kdevtmpfs]
root 12 2 0 Dec18 ? 00:00:00 [netns]
root 273 2 0 Dec18 ? 00:00:00 [writeback]
root 275 2 0 Dec18 ? 00:00:00 [crypto]
root 276 2 0 Dec18 ? 00:00:00 [bioset]
root 278 2 0 Dec18 ? 00:00:00 [kblockd]
root 287 2 0 Dec18 ? 00:00:00 [ata_sff]
root 306 2 0 Dec18 ? 00:00:00 [md]
root 395 2 0 Dec18 ? 00:00:00 [rpciod]
root 407 2 0 Dec18 ? 00:03:35 [kswapd0]
root 408 2 0 Dec18 ? 00:00:00 [fsnotify_mark]
root 472 2 0 Dec18 ? 00:00:00 [nfsiod]
root 478 2 0 Dec18 ? 00:00:00 [cifsiod]
root 1093 2 0 Dec18 ? 00:00:00 [scsi_eh_0]
root 1094 2 0 Dec18 ? 00:00:00 [scsi_tmf_0]
root 1095 2 0 Dec18 ? 00:00:00 [scsi_eh_1]
root 1098 2 0 Dec18 ? 00:00:00 [scsi_tmf_1]
root 1101 2 0 Dec18 ? 00:00:00 [scsi_eh_2]
root 1102 2 0 Dec18 ? 00:00:00 [scsi_tmf_2]
root 1105 2 0 Dec18 ? 00:00:00 [scsi_eh_3]
root 1106 2 0 Dec18 ? 00:00:00 [scsi_tmf_3]
root 1107 2 0 Dec18 ? 00:00:00 [scsi_eh_4]
root 1111 2 0 Dec18 ? 00:00:00 [scsi_tmf_4]
root 1113 2 0 Dec18 ? 00:00:00 [target_completi]
root 1115 2 0 Dec18 ? 00:00:00 [tmr-rd_mcp]
root 1118 2 0 Dec18 ? 00:00:00 [xcopy_wq]
root 1131 2 0 Dec18 ? 00:00:00 [irq/29-d00d0000]
root 1234 2 0 Dec18 ? 00:00:00 [raid5wq]
root 1238 2 0 Dec18 ? 00:00:00 [dm_bufio_cache]
root 1277 2 0 Dec18 ? 00:00:00 [ipv6_addrconf]
root 1292 2 0 Dec18 ? 00:00:00 [bioset]
root 1296 2 0 Dec18 ? 00:00:00 [deferwq]
root 1402 2 0 Dec18 ? 00:00:00 [ubi_bgt0d]
root 1471 2 7 Dec18 ? 04:36:02 [kworker/0:1H]
root 1479 2 0 Dec18 ? 00:00:00 [bioset]
root 1480 2 0 Dec18 ? 00:00:16 [md0_raid1]
root 1489 2 0 Dec18 ? 00:00:00 [bioset]
root 1490 2 0 Dec18 ? 00:00:00 [md1_raid6]
root 1495 2 0 Dec18 ? 00:00:10 [jbd2/md0-8]
root 1496 2 0 Dec18 ? 00:00:00 [ext4-rsv-conver]
root 1519 1 0 Dec18 ? 00:00:39 /lib/systemd/systemd-journald
root 1539 1 0 Dec18 ? 00:00:00 /sbin/udevd
root 1563 2 0 Dec18 ? 00:00:00 [bioset]
root 1564 2 20 Dec18 ? 12:06:59 [md127_raid5]
root 1588 2 0 Dec18 ? 00:00:00 [bioset]
root 1590 2 22 Dec18 ? 13:02:18 [md126_raid5]
root 1605 2 0 Dec18 ? 00:00:00 [bioset]
root 1606 2 0 Dec18 ? 00:00:04 [md125_raid1]
root 1642 2 0 Dec18 ? 00:00:00 [btrfs-worker]
root 1645 2 0 Dec18 ? 00:00:00 [kworker/u3:0]
root 1653 2 0 Dec18 ? 00:00:00 [btrfs-worker-hi]
root 1660 2 0 Dec18 ? 00:00:00 [btrfs-delalloc]
root 1676 2 0 Dec18 ? 00:00:00 [btrfs-flush_del]
root 1686 2 0 Dec18 ? 00:00:00 [btrfs-cache]
root 1692 2 0 Dec18 ? 00:00:00 [btrfs-submit]
root 1701 2 0 Dec18 ? 00:00:00 [btrfs-fixup]
root 1709 2 0 Dec18 ? 00:00:00 [btrfs-endio]
root 1720 2 0 Dec18 ? 00:00:00 [btrfs-endio-met]
root 1728 2 0 Dec18 ? 00:00:00 [btrfs-endio-met]
root 1737 2 0 Dec18 ? 00:00:00 [btrfs-endio-rai]
root 1745 2 0 Dec18 ? 00:00:00 [btrfs-endio-rep]
root 1752 2 0 Dec18 ? 00:00:00 [btrfs-rmw]
root 1771 2 0 Dec18 ? 00:00:00 [btrfs-endio-wri]
root 1782 2 0 Dec18 ? 00:00:00 [btrfs-freespace]
root 1791 2 0 Dec18 ? 00:00:00 [btrfs-delayed-m]
root 1796 2 0 Dec18 ? 00:00:00 [btrfs-readahead]
root 1804 2 0 Dec18 ? 00:00:00 [btrfs-qgroup-re]
root 1807 2 0 Dec18 ? 00:00:00 [btrfs-extent-re]
root 2790 2 0 Dec18 ? 00:00:00 [btrfs-cleaner]
root 2791 2 0 Dec18 ? 00:00:01 [btrfs-transacti]
root 2801 1 0 Dec18 ? 00:00:00 /usr/sbin/sshd -D
root 2802 1 0 Dec18 ? 00:00:01 /usr/sbin/mdcsrepaird -v
root 2803 1 0 Dec18 ? 00:00:00 /sbin/mdadm -F -s -y -p /frontview/bin/md_event
root 2804 1 0 Dec18 ? 00:00:00 /usr/sbin/cron -f
avahi 2806 1 0 Dec18 ? 00:01:30 avahi-daemon: running [readynas.local]
root 2809 1 0 Dec18 ? 00:00:00 /usr/sbin/raidard -S
root 2812 1 0 Dec18 ? 00:00:27 /usr/sbin/minidlnad -S
root 2814 1 0 Dec18 ? 00:00:00 /opt/p2p/bin/leafp2p -n
root 2817 1 0 Dec18 ? 00:00:01 /usr/sbin/connmand -n
83 2819 1 0 Dec18 ? 00:00:00 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
root 2826 1 0 Dec18 ? 00:00:00 /lib/systemd/systemd-logind
avahi 2827 2806 0 Dec18 ? 00:00:00 avahi-daemon: chroot helper
root 2828 1 0 Dec18 tty1 00:00:00 /sbin/agetty --noclear tty1 38400
root 2831 1 0 Dec18 ttyS0 00:00:00 /sbin/agetty -s ttyS0 115200 38400 9600
media 2864 1 0 Dec18 ? 00:09:54 /usr/sbin/forked-daapd -f
root 2878 1 0 Dec18 ? 00:00:00 /opt/xcloud/bin/xagent --log_error --disable_log_file -c /opt/xcloud/etc/xagent.conf --hardware_id 3EPC48E200757 --model_id ReadyNAS 104
root 2880 1 0 Dec18 ? 00:00:13 /usr/sbin/netatalk
root 2882 2814 0 Dec18 ? 00:13:12 /opt/p2p/bin/leafp2p -n
root 2894 2880 0 Dec18 ? 00:00:07 /usr/sbin/afpd -d -F /etc/netatalk/afp.conf
root 2895 2880 0 Dec18 ? 00:00:00 /usr/sbin/cnid_metad -d -F /etc/netatalk/afp.conf
root 2905 1 0 Dec18 ? 00:00:16 /usr/sbin/nmbd
root 2931 2 0 Dec18 ? 00:00:00 [kworker/u3:1]
root 2935 1 0 Dec18 ? 00:00:13 /usr/sbin/smbd
root 2936 1 0 Dec18 ? 00:00:00 /bin/sh /usr/bin/mysqld_safe
root 3265 1 0 Dec18 ? 00:00:13 /usr/sbin/apache2 -k start
root 3292 1 1 Dec18 ? 00:41:53 /usr/sbin/readynasd -v 3 -t
mysql 3451 2936 0 Dec18 ? 00:08:13 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib/mysql/plugin --user=mysql --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/run/mysqld/mysqld.sock --port=3306
root 3452 2936 0 Dec18 ? 00:00:00 logger -t mysqld -p daemon.error
admin 3808 3265 0 Dec19 ? 00:00:31 /usr/sbin/apache2 -k start
admin 3937 3265 0 Dec19 ? 00:00:19 /usr/sbin/apache2 -k start
root 3966 3265 0 Dec18 ? 00:00:01 apache_log
root 3967 3265 0 Dec18 ? 00:00:02 apache_log
root 3968 3265 0 Dec18 ? 00:07:14 /usr/sbin/apache2 -k start
admin 3969 3265 0 Dec18 ? 00:00:43 /usr/sbin/apache2 -k start
admin 3970 3265 0 Dec18 ? 00:00:43 /usr/sbin/apache2 -k start
root 3980 1 0 Dec18 ? 00:00:02 /frontview/bin/fvbackup-q
root 3987 1 0 Dec18 ? 00:00:00 /opt/readycloud/bin/rcbrokerd -v 3
root 3990 1 0 Dec18 ? 00:00:21 /usr/sbin/minissdpd
daemon 3991 1 0 Dec18 ? 00:00:00 /usr/sbin/upnphttpd
admin 4088 3265 0 Dec18 ? 00:00:44 /usr/sbin/apache2 -k start
root 5085 2801 0 Dec18 ? 00:00:05 sshd: root@pts/0
root 5087 5085 0 Dec18 pts/0 00:00:00 -bash
mike 5435 2935 0 Dec18 ? 00:03:18 /usr/sbin/smbd
root 5617 2801 0 Dec18 ? 00:00:05 sshd: root@pts/1
root 5623 5617 0 Dec18 pts/1 00:00:00 -bash
root 5923 1539 0 Dec18 ? 00:00:00 /sbin/udevd
root 5935 1539 0 Dec18 ? 00:00:00 /sbin/udevd
admin 6554 3265 0 Dec19 ? 00:00:16 /usr/sbin/apache2 -k start
root 7879 5087 0 Dec18 pts/0 00:00:04 sh runit
admin 8509 3265 0 Dec19 ? 00:00:30 /usr/sbin/apache2 -k start
root 12253 2 0 16:01 ? 00:00:02 [kworker/0:3]
admin 15474 3265 0 00:51 ? 00:00:14 /usr/sbin/apache2 -k start
root 15492 2 0 17:43 ? 00:00:01 [kworker/0:0]
root 15804 2 0 18:03 ? 00:00:30 [kworker/u2:2]
root 16867 2 1 19:20 ? 00:00:23 [kworker/u2:6]
root 16951 2 1 19:26 ? 00:00:18 [kworker/u2:0]
guest 16965 2935 22 19:27 ? 00:04:49 /usr/sbin/smbd
root 16992 2 1 19:28 ? 00:00:16 [kworker/u2:4]
root 17080 2 1 19:35 ? 00:00:11 [kworker/u2:3]
root 17180 2 0 19:42 ? 00:00:00 [kworker/0:2]
root 17219 2 2 19:45 ? 00:00:06 [kworker/u2:1]
root 17249 2 0 19:48 ? 00:00:00 [kworker/0:1]
admin 17256 3937 0 19:48 ? 00:00:00 /frontview/lib/dbbroker.cgi
root 17262 7879 0 19:48 pts/0 00:00:00 ps -ef
admin 19293 3265 0 Dec19 ? 00:00:25 /usr/sbin/apache2 -k start
admin 28539 3265 0 07:40 ? 00:00:09 /usr/sbin/apache2 -k start

The job was set to run every 300 seconds - so it crashed within around 300 seconds of that