linux-kernel - Re: [pchecks v2 2/2] percpu: Add preemption checks to __this

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Date:	Wed, 25 Sep 2013 16:40:07 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Ingo Molnar <mingo@...nel.org>
cc:	Tejun Heo <tj@...nel.org>, akpm@...uxfoundation.org,
	linux-arch@...r.kernel.org, Steven Rostedt <srostedt@...hat.com>,
	linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [pchecks v2 2/2] percpu: Add preemption checks to __this_cpu
 ops

On Tue, 24 Sep 2013, Ingo Molnar wrote:

> Ok, this variant looks pretty good, modulo testing. I'd do:
>
>   s/check_preemption/check_preemption_disabled
>
> but that's a minor detail.

Sure.

> > +config DEBUG_THIS_CPU_OPERATIONS
> > +	bool "Debug __this_cpu operations"
> > +	depends on DEBUG_PREEMPT
> > +	default n
> > +	help
> > +	  Enables preemption checks for __this_cpu macros. These
> > +	  are macros to generate single instruction operations on
> > +	  per cpu data. The option only affects the __this_cpu variant
> > +	  which is used when fallback to multiple instructions without
> > +	  other synchronization is possible. A verification is then
> > +	  done to make sure that the thread cannot be preempted.
>
> I don't think there's a need to make this a separate preemption debug
> option: smp_processor_id() is really just a subset of the checks.

I think this is necessary since it seems that the discussions on how to do
the raw_cpu conversions may take some time. If we enable it by default
then there will be numerous new log messages. That way a developer can
enable it for working on this.

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