linux-kernel - Hang on "echo b > /proc/sysrq-trigger"

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Date:	Sat, 18 Feb 2012 11:54:25 +1300
From:	Keith Chew <keith.chew@...il.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Hang on "echo b > /proc/sysrq-trigger"

Hi

To test the reliability of a hardware, I have a script which reboots a
machine every 15 minutes after boot up. This machine has a dual video
output, VGA and DVI-D, both driven via an intel GM45 chipset (I am
using kernel 2.6.39.24 kernel intel drivers).

Some interesting results (which can be reproduced consistently):
"echo b > /proc/sysrq-trigger" via DVI-D - after 2-3 days, it hangs
(freezes) before reboot (dmesg only shows "Resetting...", nothing
after that, no panic, stack trace, etc)
"echo b > /proc/sysrq-trigger" via VGA - runs > 1 week
"reboot -fn" via VGA or DVI-D - runs > 1 week
"reboot" via VGA or DVI-D - runs > 1 week

I suspect that the intel graphics driver is not happy with the "echo b
> /proc/sysrq-trigger" when it is still running.

I would like to make the "echo b" successfully reboot the machine, but
this would appear to be a hardware bug? Is there anything that can be
done in the kernel to make the "echo b" successfully work 100%?

Regards
Keith
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