[PATCH v2 3/5] ARM: add support for kernel mode NEON

[Ard Biesheuvel]

On 26 June 2013 14:52, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
> On 26 June 2013 14:40, Will Deacon <will.deacon at arm.com> wrote:
>> On Wed, Jun 26, 2013 at 12:28:49PM +0100, Ard Biesheuvel wrote:
>>> So can you suggest a better way of making sure schedule_debug() shoots
>>> us down if calling schedule() between kernel_neon_begin and
>>> kernel_neon_end, even on non-preempt builds?
>>
>> With what we currently have in the kernel, no, I can't think of a better
>> way. However, I also don't think that smuggling in a back-end hack is a good
>> idea either. How about we follow x86's lead on this and rely on the caller
>> not to sleep for the timebeing? Then, separately to this patch series, you
>> could look at augmenting the scheduler so that schedule_debug can complain
>> if it encounters a task that is not expected to sleep? That seems like the
>> right place to fix this problem, and will benefit other architectures too.
>>
>
> Good point. As preempt_enable/disable already have this side effect on
> PREEMPT builds, perhaps it wouldn't be such a bad idea to modify them
> in the non-PREEMPT case to at least complain if schedule() is invoked
> during such a section.
>

It appears we have this already, but in the non-PREEMPT case, it needs
CONFIG_DEBUG_ATOMIC_SLEEP to be defined.
Let's just rely on preempt_disable() to do the right thing...

-- 
Ard.


> @Russell: you mentioned spinlocks at some point to prevent sleeping.
> Are you ok with Will's suggestion instead, i.e., to rely on
> preempt_disable() to do the right thing, and fix it later because
> currently, it doesn't on non-PREEMPT?
>
> --
> Ard.