Re: Real-Time Preemption, -RT-2.6.12-final-V0.7.51-06

[William Weston <weston@sysex.net>]

On Thu, 7 Jul 2005, Ingo Molnar wrote:

> > Still looking into this issue on -51-06.  Found something really odd: 
> > SCHED_NORMAL tasks will start to inherit the priority value of some 
> > other SCHED_FIFO task.  If JACK is started at a given SCHED_FIFO 
> > priority, X and all of its children will inherit the same priority 
> > value after login.  Other random processes will inherit this, too -- 
> > sometimes init...
> > 
> > SCHED_NORMAL tasks suddenly inheriting priority values in the range 
> > normally reserved for SCHED_FIFO could explain at least part of the 
> > meltdown I've been seeing.  Any thoughts?
> 
> is this inheritance perpetual? It is normal for some tasks to be boosted 
> momentarily, but if the condition remains even after jackd has exited, 
> it's clearly an anomaly. (lets call it "RT priority leakage".) Priority 
> leakage on SMP was fixed recently, but there could be other bugs 
> remaining.

Yes, this leakage perpetual.  That's what struck me as odd.

> There's priority-leakage debugging code in the -RT kernel, which is 
> activated if you enable CONFIG_DEBUG_PREEMPT. This debugging code, if 
> triggered, should produce 'BUG: comm/123 leaked RT prio 123 (123)?" type 
> of messages. But ... due to a bug it would not print out anything but 
> would lock up hard if it detects the condition (and if 
> RT_DEADLOCK_DETECT is enabled). I have fixed this reporting bug in the 
> -51-08 kernel.

-51-08 is building now.  I'll check out the latest, too.

--ww
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