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 <559BCBDB.7080208@xenomai.org> <559CFBE7.3050802@siemens.com>
From: Philippe Gerum <rpm@xenomai.org>
Message-ID: <559D0FEC.8030606@xenomai.org>
Date: Wed, 8 Jul 2015 13:56:28 +0200
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Subject: Re: [Xenomai] Mayday issues again
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To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Xenomai <xenomai@xenomai.org>

On 07/08/2015 12:31 PM, Jan Kiszka wrote:
> On 2015-07-07 14:53, Philippe Gerum wrote:
>> On 07/07/2015 11:27 AM, Philippe Gerum wrote:
>>> I tested the patch on ARM. Enabling IPIPE_DEBUG_INTERNAL there reveals a
>>> bug with the mayday handler now turning hw IRQs on, as a result of
>>> relaxing over the low level IRQ trampoline, which makes some I-pipe call
>>> in the irq_handler boilerplate code unhappy. The very same issue is
>>> looming on x86, with an unprotected call to __ipipe_root_p from
>>> __ipipe_handle_irq(). Disabling IRQs before leaving the mayday handler
>>> is required at the very least.
>>>
>>
>> Looking further, ARM is affected because it does not invoke
>> __ipipe_call_mayday() for triggering the mayday trap, but still uses the
>> open-coded method. This routine preserves the current hw state across
>> the trap, which should make x86 safe in the end.
> 
> Which kernel version are you testing? It's not reproducing on 3.14 for
> Cortex-A7/15 targets at least. And I find __ipipe_call_mayday in both
> 3.14 and 3.18 (fastcall_exit_check).
> 

Looking at the code, any kernel version since 3.10 will have the same
issue, older ones likely too, tested on 3.18.12. This does not depend on
the ARM target.

irq_handler from entry-armv.S:
	=> __ipipe_grab_irq (or indirecty via ipipe_handle_multi_irq with
MULTI_IRQ enabled)
		=> __ipipe_exit_irq (open coded __ipipe_notify_trap(MAYDAY),
xnthread_relax() re-enables hw IRQs)
	=> __ipipe_check_root_interruptible (from irq_handler)
		BAD: __ipipe_root_p tested with CPU migration enabled

-- 
Philippe.