ARM: domains: Possible regression in v7-M

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Wed, Sep 09, 2015 at 03:25:41PM -0300, Ariel D'Alessandro wrote:
> Russell,
> 
> El 09/09/15 a las 14:52, Russell King - ARM Linux escribi?:
> > On Wed, Sep 09, 2015 at 02:28:53PM -0300, Ariel D'Alessandro wrote:
> >> Doing a bisect I've observed that regression appears to be caused by:
> >>
> >> commit 1eef5d2f1b461c120bcd82077edee5ec706ac53b
> >> Author: Russell King <rmk+kernel@arm.linux.org.uk>
> >> Date:   Wed Aug 19 21:23:48 2015 +0100
> >>
> >>     ARM: domains: switch to keeping domain value in register
> >>
> >>
> >> Stacktrace paste below.
> >>
> >> [    0.171071] Unhandled exception: IPSR = 00000006 LR = fffffff1
> > 
> > This looks to be ARMv7M, which is nommu...  I guess what's causing this
> > is this change in arch/arm/kernel/process.c:
> > 
> > +       /*
> > +        * Copy the initial value of the domain access control register
> > +        * from the current thread: thread->addr_limit will have been
> > +        * copied from the current thread via setup_thread_stack() in
> > +        * kernel/fork.c
> > +        */
> > +       thread->cpu_domain = get_domain();
> > +
> > 
> > which probably needs to be #ifdef'd out for !MMU.  Can you try adding:
> > 
> > #ifndef CONFIG_MMU
> 
> I think you meant #ifdef CONFIG_MMU.
> 
> > ...
> > #endif
> > 
> > around that please?  Thanks.
> > 
> 
> Yeah, that works!
> 
> Added:
> 
> #ifdef CONFIG_MMU
> ...
> #endif
> 
> around that code block and it booted.

Thanks.  I've settled on using CONFIG_CPU_USE_DOMAINS here, as it only
makes sense to save this value if that option is set, and it won't be
set for noMMU platforms.

Thanks for reporting this and confirming the problem site.  If you're
okay with it, I'll add:

Reported-by: Ariel D'Alessandro <ariel@vanguardiasur.com.ar>

to the commit to acknowledge your help in finding this.

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