linux-kernel - Re: [PATCHSET] ptrace,signal: group stop / ptrace updates

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Message-ID: <20110128183650.GA26633@Krystal>
Date:	Fri, 28 Jan 2011 13:36:50 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Anca Emanuel <anca.emanuel@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	Tejun Heo <tj@...nel.org>, roland@...hat.com, oleg@...hat.com,
	jan.kratochvil@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frédéric Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCHSET] ptrace,signal: group stop / ptrace updates

* Anca Emanuel (anca.emanuel@...il.com) wrote:
> On Fri, Jan 28, 2011 at 7:41 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > On Fri, 28 Jan 2011, Ingo Molnar wrote:
> >> See that '^C^C' line? That is where i had to do Ctrl-C twice.
> >>
> >> It only fails here about once every 10 times, so it's very rare. I have a stock F14
> >> system running on that box, with the very latest .38 based kernel.
> >
> > Tripped over the refuse ^C thing today twice. Had to kill a kernel
> > build from another shell. It just happily displayed ^C and never
> > stopped. That happens once in a while and I have no idea either how to
> > debug that.
> 
> cc: Mathieu
> 
> Use lttng ?

Heh :) I'm sure Ingo and Thomas have their own tools for that ;) There is
one extra thing in the LTTng instrumentation that can help solve this problem:
the "input subsystem" instrumentation (enabled with ltt-armall -i). You can then
get a dump of:

- Your keystrokes (you can then grep for your ctrl-c input)
- Read/poll/select system calls (so you know when your terminal receives the
  input).
- Signals sent/delivered

Some of these are already instrumented in the mainline kernel, so you might get
away without the input subsystem instrumentation.

If I had to take a wild guess, my bet would be to take a look in the area of
signal delivery, but you never know, maybe it's a userspace bug in the X
terminal emulator code that is causing this weirdness.

Hope this helps,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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