How to hang 2.6.9 using serial port and FB console

How to hang 2.6.9 using serial port and FB console

[Karel Kulhavy]

Hello

1) Obtain gentoo LiveCD 2004.3 which contains kernel 2.6.9-gentoo-r1
2) Obtain remote controller "YAMAHA REMOTE CONTROL TRANSMITTER RCX"
from "YAMAHA NATURAL SOUND STEREO RECEIVER RX-360 =RS"
3) Obtain an IrDA dongle based on datasheet circuit of HSDL3612
4) Obtain a motherboard with IrDA connector
5) Enable IrDA in BIOS, set up RX active Lo and TX active Hi and Full Duplex
(on my board, FIC VA503+ with 400MHz Athlon it was COM2 alias /dev/ttyS1)
6) Boot up the "gentoo" kernel from the LiveCD
7) Do stty -F /dev/ttyS1 ispeed 19200 ospeed 19200
8) Do hexdump /dev/ttyS1 on console 2 (those without the fancy graphics)
9) Press couple of keys on the remote control until the hexdump starts spewing
tons of characters continuously even when you don't press anything.
Switch to console 3 and back. Nothing happens.
10) Break the hexdump and run the cat again on console 1 (with fancy graphics)
11) Press keys on remote control until hexdump starts spewing chars continuously
12) Switch to console 3
13) Try to switch back to console 1. The system stops responding:
Action       Does user notice anything?
---------------------------------------
numlock      no
capslock     no
scrolllock   no
ctrl-alt-del no
alt-sysrq-a  no
alt-sysrq-u  no
alt-sysrq-b  reboot

The board used and the hardware in the PC is for a long time in usage and
don't have any observable problems.

Cl<

Re: How to hang 2.6.9 using serial port and FB console

[Karel Kulhavy]

On Sun, Dec 26, 2004 at 03:53:50PM +0000, Dr. David Alan Gilbert wrote:
> * Karel Kulhavy (clock@twibright.com) wrote:
> > On Sun, Dec 26, 2004 at 02:53:35PM +0000, Dr. David Alan Gilbert wrote:
> > > Hi Karel,
> > >   I wonder - is the board sending a 'break' signal to the PC? I just
> > 
> > What board do you mean?
> 
> Your IR interface board.

The IR interface isn't a board. It's a HSDL3612 with 2 capacitors and one
resistor soldered in a box according to the recommended wiring from datasheet,
so technically, it's not a board, but an airwire construction ;-)

However it is not sending breaks, but rather various characters. As the kernel
seems to be set internally for echo cahracters going into the computer on the
transmit line again, and the characters are echoed by the infrared receiver
during transmission too, a character stream cycles infinitely there.

However kernel shouldn't hang even if you wired the serial input to an alien
spacecraft.

CL<

Re: How to hang 2.6.9 using serial port and FB console

[Karel Kulhavy]

On Sun, Dec 26, 2004 at 02:53:35PM +0000, Dr. David Alan Gilbert wrote:
> Hi Karel,
>   I wonder - is the board sending a 'break' signal to the PC? I just
> remember years ago you could almsot lock machines up by constantly
> sending break.

But in this case the kernel doesn't care if you run it on a console without
a fancy background picture and hangs when you run it on a fancy background
picture.

The picture is what seems to be evil here.

Cl<

Re: How to hang 2.6.9 using serial port and FB console

[Karel Kulhavy]

I found out another bit of information:

When the kernel is hanged up and I remove the infra dongle (so that
nothing is sent towards the computer anymore for sure), the kernel stays
hanging.

This is therefore a final proof that it is not caused by sending breaks.
Dongle that is not present can't send breaks anymore ;-)

Cl<
On Sun, Dec 26, 2004 at 04:24:26PM +0000, Karel Kulhavy wrote:
> On Sun, Dec 26, 2004 at 02:53:35PM +0000, Dr. David Alan Gilbert wrote:
> > Hi Karel,
> >   I wonder - is the board sending a 'break' signal to the PC? I just
> > remember years ago you could almsot lock machines up by constantly
> > sending break.
> 
> But in this case the kernel doesn't care if you run it on a console without
> a fancy background picture and hangs when you run it on a fancy background
> picture.
> 
> The picture is what seems to be evil here.
> 
> Cl<
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Re: How to hang 2.6.9 using serial port and FB console

[Pavel Machek]

Hi!

> >   I wonder - is the board sending a 'break' signal to the PC? I just
> > remember years ago you could almsot lock machines up by constantly
> > sending break.
> 
> But in this case the kernel doesn't care if you run it on a console without
> a fancy background picture and hangs when you run it on a fancy background
> picture.
> 
> The picture is what seems to be evil here.

Picture is not in vanilla kernel => complain to gentoo.
									Pavel
-- 
People were complaining that M$ turns users into beta-testers...
...jr ghea gurz vagb qrirybcref, naq gurl frrz gb yvxr vg gung jnl!

Re: How to hang 2.6.9 using serial port and FB console

[Russell King]

On Sun, Dec 26, 2004 at 04:21:07PM +0000, Karel Kulhavy wrote:
> However it is not sending breaks, but rather various characters. As the kernel
> seems to be set internally for echo cahracters going into the computer on the
> transmit line again, and the characters are echoed by the infrared receiver
> during transmission too, a character stream cycles infinitely there.
> 
> However kernel shouldn't hang even if you wired the serial input to an alien
> spacecraft.

How do you know if it's the serial that's causing the hang rather than
the virtual console subsystem?

Your original description seems to imply that the machine only hung after
you switched from VC1 to VC3, and then you found you couldn't switch back
to VC1.  To me, that sounds virtual console related rather than serial
related.  Especially if you can reproduce it at this exact point in time
every time.

Have you tried sysrq-p or sysrq-t to get a trace/thread info from the
kernel?

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
                 2.6 Serial core