Re: [Xenomai] ipipe: issues with ARM exception handling

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

On Fri, Feb 20, 2015 at 07:03:14PM +0100, Jan Kiszka wrote:
> Hi Gilles,

Philippe is the author of this code. My code did something dumb
along the lines of what you are suggested and he found that it in
fact did not work.

> 
> analyzing a lockdep warning on 3.16 with I-pipe enabled, I dug deeper
> into the hard and virtual interrupt state management during exception
> handling on ARM. I think there are several issues:
> 
> - ipipe_fault_entry should not fiddle with the root irq state if run
>   over head, only when invoked over root.
> - ipipe_fault_exit must not change the root state unless we entered over
>   head and are about to leave over root - see x86. The current code may
>   keep root incorrectly stalled after an exception, though this will
>   probably be fixed up again in practice quickly.
> - do_sect_fault is only called by do_DataAbort and do_PrefetchAbort,
>   in both cases already wrapped in ipipe_fault_entry/exit, thus it
>   shouldn't invoke them once again.
> 
> Room for optimization:
> - ipipe_fault_entry is always called with hard IRQs off from
>   do_page_fault and do_translation_fault. I suspect this applies to the
>   remaining callers (do_DataAbort and do_PrefetchAbort ) as well. Thus
>   the hard IRQ state is actually known at compile time, right?
> 
> I can hack up patches, but I'd like to confirm first that I'm not
> missing anything subtle or ARM-specific here.
> 
> Jan

-- 
					    Gilles.