Hi Eric,

I fall in a general protection fault with setns:

general protection fault: 0000 [#3] DEBUG_PAGEALLOC
last sysfs file: /sys/devices/virtual/net/sit0/type
CPU 0
Pid: 6843, comm: myattach2 Tainted: G      D    2.6.33 #239 /
RIP: 0010:[<ffffffff810e01d0>]  [<ffffffff810e01d0>] 
d_hash_and_lookup+0x3d/0x73
RSP: 0018:ffff880034aefd28  EFLAGS: 00010246
RAX: 0000000000019cac RBX: ffff880034aefd78 RCX: 0000000000000000
RDX: ffff880034aefd8a RSI: 0000000000000303 RDI: 0000000000000003
RBP: ffff880034aefd38 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000200000000 R12: 6b6b6b6b6b6b6b6b
R13: ffff8800383ef740 R14: 0000000000000014 R15: ffff880034aefd78
FS:  00007f94377816f0(0000) GS:ffffffff8161b000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00007fb88fb8c050 CR3: 0000000034a95000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process myattach2 (pid: 6843, threadinfo ffff880034aee000, task 
ffff88003d679048)
Stack:
  ffff880034aefd88 0000000000000001 ffff880034aefdc8 ffffffff8111712a
<0> ffff880034aefdc8 0000000000000046 0000000000000000 ffff8800349dcac0
<0> 0000001400000000 ffff8800349dcac0 0000000200019cac ffff880034aefd88
Call Trace:
  [<ffffffff8111712a>] proc_flush_task+0x8e/0x283
  [<ffffffff8102e4c7>] release_task+0x24/0x30f
  [<ffffffff8102ece3>] wait_consider_task+0x531/0x923
  [<ffffffff8102f1c2>] do_wait+0xed/0x213
  [<ffffffff81043342>] ? find_get_pid+0x0/0x66
  [<ffffffff8102f380>] sys_wait4+0x98/0xbb
  [<ffffffff8102daec>] ? child_wait_callback+0x0/0x53
  [<ffffffff810028e8>] system_call_fastpath+0x16/0x1b
Code: 48 8b 56 08 eb 1f 0f b6 32 ff c9 48 ff c2 48 89 f7 48 c1 e6 04 48 
c1 ef 04 48 8d 34 37 48 8d 04 06 48 6b c0 0b 85 c9 75 dd 89 03 <49> 8b 
84 24 b8 00 00 00 48 85 c0 74 19 48 8b 40 08 48 85 c0 74
RIP  [<ffffffff810e01d0>] d_hash_and_lookup+0x3d/0x73
  RSP <ffff880034aefd28>
---[ end trace 2a26f2e5384ecec1 ]---

That happens when creating a container, attach to it and then kill the 
container.

The program doing the attach is in "attachement" :)

That happens if you do:

    setns()
    fork(), exec(mycmd).
    waitpid().


Without the fork / waitpid, that is the current process does exec, the 
problem does not occur.