[patch] Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.31-17

[Ingo Molnar <mingo@elte.hu>]

* Wen-chien Jesse Sung <jesse@cola.voip.idv.tw> wrote:

> I redo the test with a vanilla 2.6.10-rc2-mm3-V0.7.31-16 again, and it
> still hangs at hwclock. Here's the complete config file.

ok, could you try the -17 kernel i've just uploaded to the usual place:

    http://redhat.com/~mingo/realtime-preempt/

does this fix the lockup?

i believe the lockup is an interesting side-effect of threading IRQ#0:
any code within the kernel that loops on jiffies will produce a lockup,
because it starves the timer IRQ thread.

The RTC driver had two such places, but i also found one in the
IRQ-autodetect code. We want to eliminate such code anyway, and a lockup
is certainly an effective way to detect it ;)

to debug such lockups in the future you can do:

	echo 1 > /proc/sys/kernel/debug_direct_keyboard
	/sbin/hwclock ...

and use the sysrq keys to get a stack dump of the lockup. NOTE: dont use
the keyboard in this mode for too long, it can lock up.

	Ingo