ARM: domains: Possible regression in v7-M

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

On Wed, Sep 09, 2015 at 02:28:53PM -0300, Ariel D'Alessandro wrote:
> Hi,
> 
> I'm testing next-20150909 on a Hitex LPC4350 Evaluation Board, which has
> an ARMv7 Cortex-M4 processor.
> 
> There's a problem when booting using the attached config. Config is
> lpc18xx_defconfig with dram setting for the Hitex Board.
> 
> 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
...
#endif

around that please?  Thanks.

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