Querying autofs (systemd-managed nfs) mounts causes kernel hang

[Surfrock66]

This is Ubuntu Server Wily, fully up to date, on a Dell PowerEdge SC1425.

System: Host: sr66-blade Kernel: 4.2.0-19-generic x86_64 (64 bit gcc: 5.2.1) Console: tty dm: lightdm
           Distro: Ubuntu 15.10 wily

I do not know if this is an NFS, autofs, systemd, kernel-related, or something else bug.

I have 7 NFS mounts in my /home/surfrock66 directory which come from a FreeNAS NFS server. These have worked fine for years. I recently switched these mounts from NFS to systemd-managed NFS (which as I understand, converts them to autofs).

/home/surfrock66/.bitcoinbackup
/home/surfrock66/.healtheducation
/home/surfrock66/.litecoinbackup
/home/surfrock66/.sr66_nas_documents
/home/surfrock66/.sr66_nas_music
/home/surfrock66/.sr66_nas_pictures
/home/surfrock66/Videos

These mounts APPEAR to mount correctly and work semi-normally; I have scripts that do automated copies from local folders to there and they succeed. However, if I log into ssh from my account, everything is fine, I end up in /home/surfrock66. if I cd into /home/surfrock66/Downloads and do a ls, I see everything fine. If I then "cd /home/surfrock66" and do an ls...the system COMPLETELY hangs. I cannot open another ssh session. Oddly enough, the web server still responds, and things like subsonic appear to continue working. If I go to an actual keyboard/mouse, I cannot do anything other than wiggle the mouse, no applications launch and I can't switch windows. If I'm tailing syslog in another session, this is the last message I see:

Dec 3 13:28:30 sr66-blade kernel: [ 6840.240134] INFO: task ls:2353 blocked for more than 120 seconds.
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240143] Not tainted 4.2.0-19-generic #23-Ubuntu
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240146] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240149] ls D ffff88041fd96640 0 2353 1 0x00000004
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240157] ffff880356147988 0000000000000082 ffff88040d66b200 ffff88040c334b00
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240163] ffff880356147978 ffff880356148000 ffff8800da135da0 ffff8800da135d98
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240168] ffff88040c334b00 ffff880407422700 ffff8803561479a8 ffffffff817ec197
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240173] Call Trace:
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240186] [<ffffffff817ec197>] schedule+0x37/0x80
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240191] [<ffffffff817ef239>] schedule_timeout+0x189/0x250
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240199] [<ffffffff810bcc59>] ? finish_wait+0x59/0x70
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240204] [<ffffffff817ee0a6>] ? mutex_lock+0x16/0x40
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240216] [<ffffffffc01a19d0>] ? autofs4_wait+0x470/0x860 [autofs4]
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240220] [<ffffffff817ecbb3>] wait_for_completion+0xb3/0x140
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240225] [<ffffffff810a5b80>] ? wake_up_q+0x70/0x70
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240231] [<ffffffffc01a2ac7>] autofs4_expire_wait+0x77/0x110 [autofs4]
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240235] [<ffffffffc019fbeb>] do_expire_wait+0x19b/0x1d0 [autofs4]
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240240] [<ffffffffc01a0082>] autofs4_d_manage+0x72/0x190 [autofs4]
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240245] [<ffffffff81207bca>] follow_managed+0x9a/0x2e0
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240248] [<ffffffff81208103>] lookup_fast+0x133/0x340
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240252] [<ffffffff81209d19>] walk_component+0x49/0x2a0
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240255] [<ffffffff8120afcd>] path_lookupat+0x5d/0x110
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240258] [<ffffffff8120cb89>] filename_lookup+0xa9/0x180
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240262] [<ffffffff812227d0>] ? vfs_getxattr+0x90/0xb0
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240266] [<ffffffff81222e21>] ? getxattr+0x181/0x200
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240270] [<ffffffff811de5a7>] ? kmem_cache_alloc+0x187/0x200
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240273] [<ffffffff8120c796>] ? getname_flags+0x56/0x1f0
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240277] [<ffffffff8120cd3a>] user_path_at_empty+0x3a/0x50
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240281] [<ffffffff81202096>] vfs_fstatat+0x66/0xc0
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240285] [<ffffffff81202661>] SYSC_newlstat+0x31/0x60
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240288] [<ffffffff81222f11>] ? path_getxattr+0x71/0xb0
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240292] [<ffffffff8120279e>] SyS_newlstat+0xe/0x10
Dec 3 13:28:30 sr66-blade kernel: [ 6840.240296] [<ffffffff817f01f2>] entry_SYSCALL_64_fastpath+0x16/0x75

I have not found a software recovery out of this, it's required a hard poweroff/poweron each time.

Here's my /etc/fstab entries

UUID=12f7b347-791a-4b95-a9d7-45c726449c51 / ext4 errors=remount-ro 0 1
# swap was on /dev/md0 during installation
UUID=346555f2-5deb-429b-aee3-cbf91162090b none swap sw 0 0
192.168.1.36:/mnt/sr66-nas-v01/Videos /home/surfrock66/Videos nfs auto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0
192.168.1.36:/mnt/sr66-nas-v01/Documents /home/surfrock66/.sr66_nas_documents nfs auto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0
192.168.1.36:/mnt/sr66-nas-v01/Pictures /home/surfrock66/.sr66_nas_pictures nfs auto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0
192.168.1.36:/mnt/sr66-nas-v01/Music /home/surfrock66/.sr66_nas_music nfs auto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0
192.168.1.36:/mnt/sr66-nas-v01/.bitcoinbackup /home/surfrock66/.bitcoinbackup nfs auto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0
192.168.1.36:/mnt/sr66-nas-v01/.litecoinbackup /home/surfrock66/.litecoinbackup nfs auto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0
192.168.1.36:/mnt/sr66-nas-v01/HealthEducation /home/surfrock66/.healtheducation nfs auto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0
#sr66-blade:/home/surfrock66 /mnt/hda nfs auto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0
sr66-darter:/home/surfrock66 /mnt/sr66-darter nfs auto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0
sr66-dell-laptop:/home/surfrock66 /mnt/sr66-dell-laptop nfs auto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0
sr66-hp:/home/surfrock66 /mnt/sr66-hp nfs auto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0
sr76:/home/surfrock66 /mnt/sr76 nfs auto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. It seems that your bug report is not filed about a specific source package though, rather it is just filed against Ubuntu in general. It is important that bug reports be filed about source packages so that people interested in the package can find the bugs about it. You can find some hints about determining what package your bug might be about at https://wiki.ubuntu.com/Bugs/FindRightPackage. You might also ask for help in the #ubuntu-bugs irc channel on Freenode.

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