On Mon, Jul 11, 2016 at 9:31 AM, Mark Rutland <mark.rutland@xxxxxxx> wrote:
>>
>> So until you do the wire that actually disables preemption you can
>> schedule away as much as you want, and after that write you no longer
>> will.
>
> I was assuming a percpu pointer to current (or preempt count).
So for the same reason that is ok *iff* you have
- some kind of dedicated percpu register (or other base pointer - x86
has the segment thing) that gets updated when you schedule.
- an instruction that can load 'current' directly off that register atomically.
But yes, percpu data in general is obviously not safe to access
without preemption.
Linus
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