Re: [Xenomai] Inconsistent traced Linux IRQ state on ARM

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On 07/14/2014 09:01 AM, Jan Kiszka wrote:
> On 2014-07-12 13:27, Gilles Chanteperdrix wrote:
>> On 07/11/2014 07:46 AM, Jan Kiszka wrote:
>>> Gilles,
>>>
>>> we see an warning about an inconsistency of the Linux IRQ state on ARM
>>> with CONFIG_PROVE_LOCKING and, thus, CONFIG_TRACE_IRQFLAGS. I just
>>> browsed code and history and stumbled over 11a959bf53 ("ipipe/arm:
>>> disable calls to trace_hardirqs_(on|off) from assembly", ipipe-3.4.6),
>>> the only obvious related delta between vanilla and the ipipe kernel. Can
>>> you comment on both why you disabled it
>>
>> The reason why I disabled it is that:
>> 1- the spots where these functions are called are spots where hardware
>> interrupts may be off, but the root stage not necessary stalled, which
>> will may be confusing;
>> 2- these spots are also deep enough in the assembly code to be called
>> for real-time tasks, which again may confuse these functions.
> 
> It's ok to remove Linux tracing from the heart of those functions if
> they are used in RT context as well. But then we should fix up the state
> when handing over to Linux again. Apparently, we are missing at least
> one fix-up here.
> 
>>
>> Since I do not really understand the need for enabling this option with
>> CONFIG_IPIPE (if you want to debug some Linux critical sections, you
>> can do it without CONFIG_IPIPE, if you are after non-virtualized hard
>> irq flags, the I-pipe tracer has an option to debug them), I simply took
>> the easy way out and removed these calls.
> 
> The need for not breaking the kernels debugging infrastructure is being
> able to analyze kernel components that use both real-time and plain
> Linux locking and interrupt infrastructure. We do have such use cases.
> It also helped in the past on x86 to validate the I-pipe patch itself.

Any patch will be welcome. But do not take too long, because the I-pipe
patch for Linux 3.14, and following that Xenomai 2.6.4 are to be
released soon.


-- 
                                                                Gilles.