Re: Hard lockup with 2.6.24.7-rt26 on x86

[Carsten Emde <Carsten.Emde@osadl.org>]

Clark,

>> On two different desktop PC (both Core 2 Duo) and on a notebook
>> (Core Duo) the kernel (2.6.24.7-rt26, CONFIG_X86_32) locks up hard
>> under a certain rt load. The failure can be reproduced reliably
>> with the following command:
>> sudo ./cyclictest -p99 -t10 -n -i250
> My guess would be that since you're running 10 threads on two 
> processors at the highest available priority, you're starving all the
> hard IRQ threads (as well as soft irq and other kernel threads).
> This is one of those power-tool moments where you can lock up the 
> system with the wrong workload/priority combination.
Hmm, I would agree immediately, if the tasks were using all of the CPU
power. But this is not the case. In the present case, running

# cyclictest -p99 -t10 -n -i250

results in about 10% CPU load. So there is plenty of time in between to
let the system respond. I can reproduce the problem here (2.6.24-rt,
2.6.26-rt, various configurations). The system does not crash every time
when cyclictest is started, only once in about 5 trials or so. If it
crashes, then it does so immediately after being started. Whenever
cyclictest survives for several seconds, then it never crashes at a
later time. I tend to believe that we have a bug here, not a regular
behavior.

	Carsten.