BUG: commit "ARM: Remove __ARCH_WANT_INTERRUPTS_ON_CTXSW on pre-ARMv6 CPUs" breaks armv5 with CONFIG_PREEMPT

[Marc Kleine-Budde]

On 06/20/2013 03:01 PM, Catalin Marinas wrote:
> On Thu, Jun 20, 2013 at 12:47:25PM +0100, Marc Kleine-Budde wrote:
>> On 06/20/2013 01:39 PM, Marc Kleine-Budde wrote:
>>> On 06/20/2013 01:35 PM, Marc Kleine-Budde wrote:
>>>> On 06/20/2013 01:12 PM, Catalin Marinas wrote:
>>>>> On Thu, Jun 20, 2013 at 11:28:56AM +0100, Catalin Marinas wrote:
>>>>>> We may need to place the preempt disable/enable at a higher level in the
>>>>>> scheduler. My theory is that we have a context switch from prev to next.
>>>>>> We get preempted just before finish_arch_post_lock_switch(), so the MMU
>>>>>> hasn't been switched yet. The new switch during preemption happens to a
>>>>>> thread with the same next mm, so the scheduler no longer switch_mm() and
>>>>>> the TIF_SWITCH_MM isn't set for the new thread.
>>>>>>
>>>>>> I'll come back with another patch shortly.
>>>>>
>>>>> Here's another attempt (as before, only compile-tested):
>>>>
>>>> booting kernel from /image
>>>> zImage: concatenated oftree detected
>>>> booting Linux kernel with devicetree
>>>>
>>>> ...dead...
>>>>
>>>> Does every process have a "mm"? Even Kernel threads?
>>
>> I've added a check for "mm". Boots now and my test runs stable for 3
>> minutes now.
> 
> Ah, good point.
> 
>> I'm not sure if we have to check for "mm" in
>> check_and_switch_context(), too.
> 
> switch_mm() wouldn't be called with a NULL mm, hence we wouldn't call
> check_and_switch_context() either. finish_arch_post_lock_switch() is
> called all the time (and we set the TIF flag only if switch_mm() was
> called).

Thanks for the explanation. $CUSTOMER's mx28 runs stable with the
minimal test program, I'll keep you informed if they have tested with
the full blown program.

Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
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