autofs4 hangs waiting to mount local file-system

[TJ]

18.04 amd64, 4.15.0-50-lowlatency.

The system has a number of local autofs mounts created and managed by systemd through .automount units.

Earlier today I had finished working on one such ("SourceCode") and it had auto-unmounted after the idle time. A short time after that I tried to use that auto-mount directory again ("/home/tj/SourceCode") and the shell hung. I tried from several more shells with different commands with the same result.

Initially couldn't see any clues in the logs but after a while the kernel dumped a couple of stack traces of which I include the first here.

After the stack-traces appeared the shell was able to report an error for other auto-mounts that haven't hung but trying to access the problematic "/home/tj/SourceCode" still hangs the shell, and trying to manually mount the affected file-system to the same location also hangs but works for another mount-point:

ls: cannot access '/home/tj/Projects/': Host is down

In trying to clean up I manually stopped all the systemd .mount/.automount units. As soon as I stopped the home-tj-SourceCode.automount unit the mount succeeded and the shells un-hung.

Not sure if this is caused by the systemd autofs handling or there was some race condition behind it, but it seems to have recovered.

Jun 24 11:01:02 T300CHI kernel: INFO: task ls:29630 blocked for more than 120 seconds.
Jun 24 11:01:02 T300CHI kernel: Tainted: G OE 4.15.0-50-lowlatency #54-Ubuntu
Jun 24 11:01:02 T300CHI kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Jun 24 11:01:02 T300CHI kernel: Call Trace:
Jun 24 11:01:02 T300CHI kernel: __schedule+0x293/0x8a0
Jun 24 11:01:02 T300CHI kernel: schedule+0x33/0x90
Jun 24 11:01:02 T300CHI kernel: schedule_timeout+0x1e6/0x380
Jun 24 11:01:02 T300CHI kernel: ? autofs4_wait+0x451/0x870 [autofs4]
Jun 24 11:01:02 T300CHI kernel: wait_for_completion+0xac/0x130
Jun 24 11:01:02 T300CHI kernel: ? wake_up_q+0x80/0x80
Jun 24 11:01:02 T300CHI kernel: autofs4_expire_wait+0xa0/0x160 [autofs4]
Jun 24 11:01:02 T300CHI kernel: do_expire_wait+0x155/0x210 [autofs4]
Jun 24 11:01:02 T300CHI kernel: ? __d_alloc+0x122/0x1d0
Jun 24 11:01:02 T300CHI kernel: autofs4_d_manage+0x76/0x1a0 [autofs4]
Jun 24 11:01:02 T300CHI kernel: follow_managed+0xce/0x310
Jun 24 11:01:02 T300CHI kernel: lookup_fast+0x115/0x340
Jun 24 11:01:02 T300CHI kernel: walk_component+0x49/0x470
Jun 24 11:01:02 T300CHI kernel: path_lookupat+0x84/0x1f0
Jun 24 11:01:02 T300CHI kernel: filename_lookup+0xb6/0x190
Jun 24 11:01:02 T300CHI kernel: ? mem_cgroup_commit_charge+0x82/0x520
Jun 24 11:01:02 T300CHI kernel: ? __check_object_size+0xaf/0x1b0
Jun 24 11:01:02 T300CHI kernel: ? strncpy_from_user+0x4d/0x170
Jun 24 11:01:02 T300CHI kernel: user_path_at_empty+0x36/0x40
Jun 24 11:01:02 T300CHI kernel: ? user_path_at_empty+0x36/0x40
Jun 24 11:01:02 T300CHI kernel: vfs_statx+0x76/0xe0
Jun 24 11:01:02 T300CHI kernel: SYSC_newstat+0x3d/0x70
Jun 24 11:01:02 T300CHI kernel: ? __do_page_fault+0x292/0x520
Jun 24 11:01:02 T300CHI kernel: SyS_newstat+0xe/0x10
Jun 24 11:01:02 T300CHI kernel: do_syscall_64+0x73/0x130
Jun 24 11:01:02 T300CHI kernel: entry_SYSCALL_64_after_hwframe+0x3d/0xa2
Jun 24 11:01:02 T300CHI kernel: RIP: 0033:0x7f4a02814775
Jun 24 11:01:02 T300CHI kernel: RSP: 002b:00007fff7c274b98 EFLAGS: 00000246 ORIG_RAX: 0000000000000004
Jun 24 11:01:02 T300CHI kernel: RAX: ffffffffffffffda RBX: 000055fb8dd08640 RCX: 00007f4a02814775
Jun 24 11:01:02 T300CHI kernel: RDX: 000055fb8dd08658 RSI: 000055fb8dd08658 RDI: 00007fff7c276d68
Jun 24 11:01:02 T300CHI kernel: RBP: 00007fff7c274f40 R08: 0000000000000000 R09: 00007fff7c276d72
Jun 24 11:01:02 T300CHI kernel: R10: 000000007c276d00 R11: 0000000000000246 R12: 00007fff7c276d68
Jun 24 11:01:02 T300CHI kernel: R13: 0000000000000001 R14: 0000000000000000 R15: 000055fb8dd08658

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1834003

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Launchpad Janitor (janitor)]

[Expired for linux (Ubuntu) because there has been no activity for 60 days.]