linux-kernel - Re: 2.6.25.3: su gets stuck for root

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Message-ID: <485323C5.4030002@skyrush.com>
Date:	Fri, 13 Jun 2008 19:49:57 -0600
From:	Joe Peterson <joe@...rush.com>
To:	Vegard Nossum <vegard.nossum@...il.com>
CC:	Alan Cox <alan@...hat.com>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	David Newall <davidn@...idnewall.com>,
	Willy Tarreau <w@....eu>,
	Harald Dunkel <harald.dunkel@...nline.de>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.25.3: su gets stuck for root

Vegard Nossum wrote:
> I think knowing the pgrps of the above processes (there is possibly
> one more involved, stty?) would be useful; try:
> 
>     $ ps -eo pid,pgrp,tpgid,user,args

OK, I performed this test again (getting the su to hang), and here is
the info:

tty_check_change: current->signal->tty = f7879800
tty_check_change: tty = f7879800
tty_check_change: tty->pgrp = f78639c0
  tty->pgrp->count = 5
  tty->pgrp->level = 0
  tty->pgrp->numbers[0].nr = 7036
tty_check_change: task_pgrp(current) = f7863f00
  task_pgrp(current)->count = 1
  task_pgrp(current)->level = 0
  task_pgrp(current)->numbers[0].nr = 7037
tty_check_change: kill_pgrp called; returning -ERESTARTSYS
set_termios: error return value (-512) from tty_check_change

scorpius ~ # ps aux | grep 7036
foo  7036  0.0  0.1   2336  1100 tty1     S+   19:30   0:00 su foo

scorpius ~ # ps aux | grep 7037
foo  7037  0.0  0.1   2988  1460 tty1     S    19:30   0:00 bash

scorpius ~ # ps -eo pid,pgrp,tpgid,user,args | grep 7036
 6902  6902  7036 root     /bin/login --
 6922  6922  7036 root     -bash
 7036  7036  7036 foo      su foo
 7037  7037  7036 foo      bash
 7042  7037  7036 foo      stty -ixany

scorpius ~ # ps -eo pid,pgrp,tpgid,user,args | grep 7037
 7037  7037  7036 foo      bash
 7042  7037  7036 foo      stty -ixany

scorpius ~ # ps aux | grep 7042
foo  7042  0.0  0.0   1608   376 tty1     T    19:30   0:00 stty -ixany

scorpius ~ # ps -eo pid,pgrp,tpgid,user,args | grep 7042
 7042  7037  7036 foo      stty -ixany

(I omitted, of course, when grep found itself, and I compressed some
white space to allow lines to fit nicely in the email)

> ..as this problem occurs because a process tries to change the
> terminal settings (and subsequently gets suspended because of that)
> while it's not the owner of the terminal.
> 
> This can happen if you fork something off to the background, e.g. like
> 
>     $ stty 9600 &
> 
> (which should immediately give you [1]+ Stopped stty 9600),
> 
> so can you please look for anything like that in your login scripts or
> shell rc files?

I do use stty in my .bashrc (that's why this happens), but I do not put
it in the background.

Anyway, hope the additional info above is of help...

					Thanks, Joe
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