[tbot] How to debug acquire_linux

[Harald Seiler]

Hi Stefano,

On Fri, 2018-11-23 at 13:16 +0100, Stefano Babic wrote:
> Hi Harald,
> 
[...]
> 
> It looks like that the additional traces change the time conditions. If
> I run with -vvv works now, without not (in both cases login_wait=1
> 
> Anyway, the output with -vvv around the login is:
> 
> 
> │   │    <>
> │   ├─< 'GTU-0 login: '
> │   ├─> 'root\n'
> │   │    <> GTU-0 login: root
> │   ├─> '\n'
> │   ├─> "PROMPT_COMMAND=''\nPS1='TBOT-VEJPVC1QUk9NUFQK$ '\n"
> │   ├─< 'root[   13.843245] NOHZ: local_softirq_pending 04\r\n[
> 13.847350] NOHZ: local_softirq_pending 04\r\n\r\r\n[   13.864221] NOHZ:
> local_softirq_pending 04\r\n[   13.868323] NOHZ: local_softirq_pending
> 04\r\n[   13.872432] NOHZ: local_softirq_pending 286\r\n[   13.888457]
> NOHZ: local_softirq_pending 80\r\n[   14.011121] NOHZ:
> local_softirq_pending 04\r\n\x1b7\x1b[r\x1b[999;999H\x1b[6n'
> │   ├─< '\x1b'
> │   ├─< '8'
> │   ├─< 'PROMPT_COMMAND='
> │   ├─< "''\r\nPS1='TBOT-VE"
> │   ├─< "JPVC1QUk9NUFQK$ '\r"
> │   ├─< '\n'
> │   ├─< 'root at GTU-0:~# '
> │   ├─< "PROMPT_COMMAND=''"
> 

Now this I can work with!  Ok, as you see, TBot sends it's shell init
commands way before the shell is up.  Somewhere they get echoed anyway,
this is to be expected.

Then, the shell comes up. It even reads the first command! But it stops there,
the command is not executed even though we sent a \n.  I guess this is a
mechanism in bash to prevent accidents ...

I guess busybox just doesn't do that which is the reason it is working there ...

I'll try to reproduce this locally and write a fix.  Can't promise I get it
done today though ...

> 
> But then works. In this case I see a kernel message (NOHZ:
> local_softirq_pending) in between.
> 
> I run 4-5 times with -vvv, it works. The race is over with the traces :-(
> 
> Best regards,
> Stefano
> 
> 
-- 
Harald

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