linux-kernel - Re: tty session leader issue (was Re: 2.6.25.3: su gets stuck for root)

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Message-ID: <alpine.DEB.1.10.0807062353450.30385@scuzzie.rather.puzzling.org>
Date:	Mon, 7 Jul 2008 00:08:58 +1000 (EST)
From:	Tim Connors <tim.w.connors@...il.com>
To:	Joe Peterson <joe@...rush.com>
cc:	Vegard Nossum <vegard.nossum@...il.com>,
	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: tty session leader issue (was Re: 2.6.25.3: su gets stuck for
 root)

On Wed, 2 Jul 2008, Joe Peterson wrote:

> I have done some more investigation on this problem, and I am posting
> here my results in hope that someone can point me in the right direction
> for further investigation...
>
> Summary: during the initialization of a new bash shell, the terminal
> foreground process group often reverts back to that of the parent of the
> bash shell (after being set *to* the bash shell pgrp by bash),
> prohibiting commands like stty from being run by the init scripts.  The
> result is that the execution of these commands will hang until killed,
> causing the bash prompt to not appear.  Adding a delay in the script
> (using sleep) increases the chance of this having time to happen.
...
> So here is the question: is there a way/reason the kernel would revert
> the pgrp of the session leader after bash sets it?  Is there some more
> instrumenting in the kernel or in bash that might reveal what is going
> on?  I have heard yet another report of this happening since I added to
> the thread, and I can get it to happen easily on two different machines
> (a desktop and a laptop).

In fact, in various laptops (Eeeepc, dell inspiron 1520, Dell inspiron
4000), I've got various tty screwups that have been introduced since
circa 2.6.19.

The 6 year old inspiron 4000 gets stuck at stty erase ^? .  Randomly, but
most of the time.

All of my machines exhibit the ctrl-C being slower than ctrl-Z discussed
elswhere (I've almost developed a habit of typing ctrl-Z kill %1 <RET>).
Although even ctrl-Z recently has been reluctant to always work.  I wonder
if this is the cause of dpkg recently not responding to ctrl-Z's? (debian
bug #486222).  dpkg does respond to kill -STOP

ctrl-s doesn't always work anymore.  Again, what prompted me to write this
email, was I couldn't pause dpkg.  It's particularly unreliable at
stopping scrolling messages at bootup, and if I press it at the wrong time
at bootup (not a specific place - it can be starting up any number of
scripts), something deadlocks and won't resume upon a ctrl-q.
alt-sysrq-k is enough to kill whatever has deadlocked.  I have a feeling,
but don't want to test on this system right now, that pressing scroll-lock
as opposed to ctrl-q once unlocked such a stuck display.

In summary, something in tty is certainly screwed.  Does anyone see a
connection between all of these?

-- 
TimC
> cat ~/.signature
Electromagnetic pulse received (core dumped)
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