Re: [gcv v3 06/35] scheduler: Replace __get_cpu_var uses

[Frederic Weisbecker]

2013/9/3 Christoph Lameter <cl@xxxxxxxxx>:
> On Thu, 29 Aug 2013, Steven Rostedt wrote:
>
>> How many places use the this_cpu_*() without preemption disabled? I
>> wouldn't think there's many. I never complained about another variant,
>> so you need to ask those that have. The tough question for me is what
>> that variant name should be ;-)
>
> Tried to add preemption checks but the basic issue is that many of the
> checks themselves use this_cpu_ops. percpu.h is very basic to the
> operation of fundamental primitives for preempt etc. Use of a BUG_ON needs
> a seris of includes in percpu.h that cause more trouble.
>
> If I switch __this_cpu ops to check for preemption then the logic for
> preemption etc must use the raw_this_cpu ops.

IIUC the issue is that preempt debug checks themselves use per cpu
operations that can result in preempt debug checks? Hence a recursion.
Do you have an example of that?

Also in this case this must be fixed anyway given the checks that
already exist in smp_processor_id(), __get_cpu_var(), ...
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