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Date: Mon, 05 May 2008 18:35:21 +0200
From: Philippe Gerum <rpm@xenomai.org>
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Sender: Philippe Gerum <philippe.gerum@domain.hid>
Subject: Re: [Xenomai-core] Houston, we have a circular problem
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To: Jan Kiszka <jan.kiszka@domain.hid>
Cc: Xenomai-core@domain.hid

Jan Kiszka wrote:
> Gilles Chanteperdrix wrote:
>> On Mon, May 5, 2008 at 6:08 PM, Philippe Gerum <rpm@xenomai.org> wrote:
>>>  do_schedule_event() is the culprit when it reads the pending signals on the
>>>  shared queue (XNDEBUG check for rearming the timers),
>> A stupid suggestion: if we know that the spinlock is always locked
>> when calling do_schedule_event, maybe we can simply avoid the lock
>> there ?
> 
> Would be the best solution - but I don't think so. After reading a bit
> more into the lockdep output, I think the issue is that _some_other_
> task my hold the siglock and then acquire our rq_lock, but not
> necessarily along a similar code path we took to acquire the siglock now.
> 

Mm, indeed. Grabbing any further kernel lock when we hold the runqueue lock is
probably a very bad idea, since any normal locking sequence would exactly go the
opposite way...

-- 
Philippe.