Badness at drivers/char/tty_ldisc.c:210 during shutdown

[Alan Cox]

> > [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