Comment 6 for bug 1403152

Kernel stack trace when lxc-start process hang:

[27211131.602770] INFO: task lxc-start:25977 blocked for more than 120 seconds.
[27211131.602785] Not tainted 3.13.0-40-generic #69-Ubuntu
[27211131.602789] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[27211131.602795] lxc-start D 0000000000000000 0 25977 1 0x00000080
[27211131.602800] ffff8806ee73dd40 0000000000000286 ffff880474bdb000 ffff8806ee73dfd8
[27211131.602803] 0000000000014480 0000000000014480 ffff880474bdb000 ffffffff81cdb760
[27211131.602806] ffffffff81cdb764 ffff880474bdb000 00000000ffffffff ffffffff81cdb768
[27211131.602809] Call Trace:
[27211131.602821] [<ffffffff81723b69>] schedule_preempt_disabled+0x29/0x70
[27211131.602825] [<ffffffff817259d5>] __mutex_lock_slowpath+0x135/0x1b0
[27211131.602832] [<ffffffff811a2679>] ? __kmalloc+0x1e9/0x230
[27211131.602835] [<ffffffff81725a6f>] mutex_lock+0x1f/0x2f
[27211131.602840] [<ffffffff8161c2c1>] copy_net_ns+0x71/0x130
[27211131.602845] [<ffffffff8108f889>] create_new_namespaces+0xf9/0x180
[27211131.602848] [<ffffffff8108f983>] copy_namespaces+0x73/0xa0
[27211131.602851] [<ffffffff81065b16>] copy_process.part.26+0x9a6/0x16b0
[27211131.602854] [<ffffffff810669f5>] do_fork+0xd5/0x340
[27211131.602857] [<ffffffff810c8e8d>] ? call_rcu_sched+0x1d/0x20
[27211131.602859] [<ffffffff81066ce6>] SyS_clone+0x16/0x20
[27211131.602863] [<ffffffff81730089>] stub_clone+0x69/0x90
[27211131.602865] [<ffffffff8172fd2d>] ? system_call_fastpath+0x1a/0x1f
[27211131.602869] INFO: task lxc-start:26342 blocked for more than 120 seconds.
[27211131.602874] Not tainted 3.13.0-40-generic #69-Ubuntu