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Date: Thu, 19 Jul 2007 14:40:05 +0200
From: Jan Kiszka <jan.kiszka@domain.hid>
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Subject: Re: [Xenomai-help] Sporadic PC freeze after rt_task_start
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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?
>=20
> 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 second=
s
> otherwise. (See the NOSWITCH bit).

OK, then it's not the cause.

>=20
>> 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 ho=
pe
>> there is none)
>=20
> xnshadow_start().

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

>=20
>> , but such nesting is already evil per se...
>=20
> Well, nesting spinlocks only falls into evilness when you get a circula=
r
> 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


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