If I have umask 007 (or any other value that masks the world-execute bit) when I run lxc-start for the first time after logging in, my host system enters a state with the following problems:
* lxc-stop hangs forever instead of stopping any container, even one that wasn't started with umask 007. * lxc-stop --kill --nolock hangs in the same way. * Attempts to reboot or shut down the host system fail, requiring a hard reset to recover. When lxc-stop hangs, messages like these appear in syslog every couple of minutes: Nov 22 14:36:55 xenialbox kernel: [ 484.506570] INFO: task systemd:3086 blocked for more than 120 seconds. Nov 22 14:36:55 xenialbox kernel: [ 484.506578] Not tainted 4.9.0-040900rc6-generic #201611201731 Nov 22 14:36:55 xenialbox kernel: [ 484.506579] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Nov 22 14:36:55 xenialbox kernel: [ 484.506582] systemd D 0 3086 3076 0x00000104 Nov 22 14:36:55 xenialbox kernel: [ 484.506589] ffff8eaa1810bc00 ffff8eaa58f4d800 ffff8eaa57f59d00 ffff8eaa5fc19340 Nov 22 14:36:55 xenialbox kernel: [ 484.506593] ffff8eaa54bec880 ffff9bab80f17b78 ffffffff8bc87183 ffffffff8c244480 Nov 22 14:36:55 xenialbox kernel: [ 484.506596] 00ff8eaa57f59d00 ffff8eaa5fc19340 0000000000000000 ffff8eaa57f59d00 Nov 22 14:36:55 xenialbox kernel: [ 484.506600] Call Trace: Nov 22 14:36:55 xenialbox kernel: [ 484.506622] [<ffffffff8bc87183>] ? __schedule+0x233/0x6e0 Nov 22 14:36:55 xenialbox kernel: [ 484.506626] [<ffffffff8bc87666>] schedule+0x36/0x80 Nov 22 14:36:55 xenialbox kernel: [ 484.506629] [<ffffffff8bc8a4da>] rwsem_down_write_failed+0x20a/0x380 Nov 22 14:36:55 xenialbox kernel: [ 484.506634] [<ffffffff8b463f3e>] ? kvm_sched_clock_read+0x1e/0x30 Nov 22 14:36:55 xenialbox kernel: [ 484.506643] [<ffffffff8b6ba5e0>] ? kernfs_sop_show_options+0x40/0x40 Nov 22 14:36:55 xenialbox kernel: [ 484.506651] [<ffffffff8b8265a7>] call_rwsem_down_write_failed+0x17/0x30 Nov 22 14:36:55 xenialbox kernel: [ 484.506655] [<ffffffff8bc89b1d>] down_write+0x2d/0x40 Nov 22 14:36:55 xenialbox kernel: [ 484.506658] [<ffffffff8b639fa0>] grab_super+0x30/0xa0 Nov 22 14:36:55 xenialbox kernel: [ 484.506661] [<ffffffff8b63a58f>] sget_userns+0x18f/0x4d0 Nov 22 14:36:55 xenialbox kernel: [ 484.506663] [<ffffffff8b6ba670>] ? kernfs_sop_show_path+0x50/0x50 Nov 22 14:36:55 xenialbox kernel: [ 484.506666] [<ffffffff8b6ba89e>] kernfs_mount_ns+0x7e/0x230 Nov 22 14:36:55 xenialbox kernel: [ 484.506674] [<ffffffff8b5230b8>] cgroup_mount+0x328/0x840 Nov 22 14:36:55 xenialbox kernel: [ 484.506679] [<ffffffff8b6036f5>] ? alloc_pages_current+0x95/0x140 Nov 22 14:36:55 xenialbox kernel: [ 484.506682] [<ffffffff8b63b578>] mount_fs+0x38/0x150 Nov 22 14:36:55 xenialbox kernel: [ 484.506686] [<ffffffff8b659177>] vfs_kern_mount+0x67/0x110 Nov 22 14:36:55 xenialbox kernel: [ 484.506688] [<ffffffff8b65baf1>] do_mount+0x1e1/0xcb0 Nov 22 14:36:55 xenialbox kernel: [ 484.506691] [<ffffffff8b6330df>] ? __check_object_size+0xff/0x1d6 Nov 22 14:36:55 xenialbox kernel: [ 484.506695] [<ffffffff8b60efe7>] ? kmem_cache_alloc_trace+0xd7/0x190 Nov 22 14:36:55 xenialbox kernel: [ 484.506697] [<ffffffff8b65c8d3>] SyS_mount+0x83/0xd0 Nov 22 14:36:55 xenialbox kernel: [ 484.506700] [<ffffffff8b403b6b>] do_syscall_64+0x5b/0xc0 Nov 22 14:36:55 xenialbox kernel: [ 484.506702] [<ffffffff8bc8c46f>] entry_SYSCALL64_slow_path+0x25/0x25 When system shutdown hangs, similar messages appear on the console every couple of minutes. I can reproduce this at will on both real hardware and a freshly-installed and fully-updated host OS in VirtualBox, with either an old-ish container or a new one, and with either the current Ubuntu LTS kernel or a mainline kernel. Here is the uname ouput of the two kernels I most recently used: Linux xenialbox 4.4.0-47-generic #68-Ubuntu SMP Wed Oct 26 19:39:52 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux Linux xenialbox 4.9.0-040900rc6-generic #201611201731 SMP Sun Nov 20 22:33:21 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux I'm running lxc 2.0.5-0ubuntu1~ubuntu16.04.2 on xubuntu 16.04.1 LTS amd64. My containers are all unprivileged. My umask at container creation time does not seem to matter. As far as I have seen, my umask only matters the first time I start a container in my login session. I can work around the bug by manually setting my umask to something more permissive before I start my first container of the day, and then setting it back again, but that's rather a hassle. (Even worse, it's very easy to forget this workaround and be left with containers that can't be stopped and a host system that won't shut down cleanly.) Possibly related: when the problem is triggered, I notice that my guest instances start with no /etc/resolv.conf and no inet address. Ubuntu bug report: https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1642767 _______________________________________________ lxc-users mailing list lxc-users@lists.linuxcontainers.org http://lists.linuxcontainers.org/listinfo/lxc-users
