quoted

[c00000003cf6ba70] [c00000000040a3d0] .tty_ldisc_put+0xa4/0xf4 (unreliable)
[c00000003cf6bb10] [c00000000040a7c8] .tty_ldisc_reinit+0x38/0x80
[c00000003cf6bba0] [c00000000040b1d8] .tty_ldisc_hangup+0x190/0x260
[c00000003cf6bc40] [c000000000401090] .do_tty_hangup+0x188/0x4c0
[c00000003cf6bd20] [c000000000401440] .tty_vhangup_self+0x34/0x54
[c00000003cf6bdb0] [c00000000019236c] .sys_vhangup+0x38/0x58
[c00000003cf6be30] [c000000000008534] syscall_exit+0x0/0x40
Instruction dump:
912b0088 4bcd17bd 60000000 e87e8008 7f44d378 481c04fd 60000000 801b0008 
7c09fe70 7d200278 7c004850 54000ffe <0b000000> 7f63db78 4bd7c98d 60000000 

Ah right, so this has check has just gone in, and the code in question
has been rewritten somewhat just recently.

The check is to catch any cases where a line discipline is being freed up
but has a refcount that is non zero. I think I know what is going on here.

Alan