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SubjectRe: [patch] Real-Time Preemption, -RT-2.6.13-rc4-V0.7.53-01, High Resolution Timers & RCU-tasklist features
Ingo Molnar wrote:
> * Ingo Molnar <mingo@elte.hu> wrote:
>
>
>>* George Anzinger <george@mvista.com> wrote:
>>
>>
>>>Ingo, all
>>>
>>>I, silly person that I am, configured an RT, SMP, PREEMPT_DEBUG system.
>>> Someone put code in the NMI path to modify the preempt count which,
>>>often as not will generate a PREEMPT_DEBUG message as there is no tell
>>>what state the preempt count is in on an NMI interrupt. I have sent
>>>the attached patch to Andrew on this, but meanwhile, if you want RT,
>>>SMP, PREEMPT_DEBUG you will be much better off with this.
>>
>>ah - thanks, applied. Might explain some of the recent SMP weirdnesses
>>i'm seeing. Attributed them to the HRT patch ;-)
>
>
> i'm still seeing weird crashes under SMP, which go away if i disable
> CONFIG_HIGH_RES_TIMERS. (this after i fixed a couple of other SMP bugs
> in the HRT code) It happens sometime during the bootup, after enabling
> the network but before users can log in. There's no good debug info,
> just a hang that comes from all CPUs trying to get some debug info out
> but crashing deeply.
>
I haven't looked at this new code all that closely as yet. One thing I
did notice is that there is an assumption that the "timer being
delivered flag" can be shared between LR timers and HR timers. I
suspect this is wrong as the delivery code is in seperate threads (I
assume). This could lead to del_timer_async missing a timer.

In the prior patch we just ignored the del_timer_async issue for HR
timers (code I plan to do soon). This WAS taken care of in earlier
kernels by a reuse of one of the list link fields, but Andrew convince
me that this was _not_ good.

So, my guess, a nanosleep for an RT task (I think you said these are
promoted to HR) is completing and over writing the deliver in progress
flag for a LR timer which just happens to have a del_timer_sync going on
at the same time.
--
George Anzinger george@mvista.com
HRT (High-res-timers): http://sourceforge.net/projects/high-res-timers/
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