Re: [RFC PATCH 04/19] cpufreq: bring data structures close to their locks

[Peter Zijlstra]

On Tue, Jan 12, 2016 at 11:21:25AM +0000, Juri Lelli wrote:
> I tried to see if something like for_each_domain() can be done, but here
> we use list_for_each_entry() macro. Peter, do you mean something like
> the following?
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 78b1e2f..1a847a6 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -39,6 +39,7 @@
>  static LIST_HEAD(cpufreq_governor_list);
>  static DEFINE_MUTEX(cpufreq_governor_mutex);
>  #define for_each_governor(__governor)				\
> +	lockdep_assert_held(&cpufreq_governor_mutex);		\
>  	list_for_each_entry(__governor, &cpufreq_governor_list, governor_list)

That fails for things like:

	if (blah)
		for_each_governor(...) {
		}

which looks like valid C -- even though our Coding Style says the if
should have { } on.

I was thinking of either open coding the for statement and adding it to
the first statement like:

	#define for_each_governor(__g) \
		for (_g = list_first_entry(&cpufreq_governor_list, typeof(*_g), governor_list, lockdep_assert_held(), \
		     ..... )

Or use something like this:

  lkml.kernel.org/r/20150422154212.GE3007@xxxxxxxxxxxxxxxxxxxxxx

	#define for_each_governor(_g) \
		list_for_each_entry(_g, &cpufreq_governor_list, governor_list)
			if (lockdep_assert_held(..), false)
				;
			else

Which should preserve C syntax rules.