Re: [Xenomai-help] Sporadic PC freeze after rt_task_start

[Jan Kiszka <jan.kiszka@domain.hid>]

[-- Attachment #1: Type: text/plain, Size: 1090 bytes --]

Philippe Gerum wrote:
>> And when looking at the holders of rpilock, I think one issue could be
>> that we hold that lock while calling into xnpod_renice_root [1], ie.
>> doing a potential context switch. Was this checked to be save?
> 
> xnpod_renice_root() does no reschedule immediately on purpose, we would
> never have been able to run any SMP config more than a couple of seconds
> otherwise. (See the NOSWITCH bit).

OK, then it's not the cause.

> 
>> Furthermore, that code path reveals that we take nklock nested into
>> rpilock [2]. I haven't found a spot for the other way around (and I hope
>> there is none)
> 
> xnshadow_start().

Nope, that one is not holding nklock. But I found an offender...

> 
>> , but such nesting is already evil per se...
> 
> Well, nesting spinlocks only falls into evilness when you get a circular
> graph, but since the rpilock is a rookie in the locking team, I'm going
> to check this.

Take this one: gatekeeper_thread calls into rpi_pop with nklock
acquired. So we have a classic ABAB locking bug. Bang!

Jan


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 250 bytes --]