On Monday, June 24, 2013 07:01:59 PM Viresh Kumar wrote:
> On 24 June 2013 19:03, Rafael J. Wysocki <rjw@xxxxxxx> wrote:
> > Looks OK, but since transition_ongoing is either 0 or 1 now, as far as I can
> > say, it would be better to make it a bool and use = true/false instead of
> > ++/-- I suppose.
>
> Another fixup:
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 6ca7eac..49d942a 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -108,7 +108,7 @@ static BLOCKING_NOTIFIER_HEAD(cpufreq_policy_notifier_list);
> static struct srcu_notifier_head cpufreq_transition_notifier_list;
>
> /* Tracks status of transition */
> -static int transition_ongoing;
> +static bool transition_ongoing;
>
> static bool init_cpufreq_transition_notifier_list_called;
> static int __init init_cpufreq_transition_notifier_list(void)
> @@ -271,7 +271,7 @@ void __cpufreq_notify_transition(struct
> cpufreq_policy *policy,
> "In middle of another frequency transition\n"))
> return;
>
> - transition_ongoing++;
> + transition_ongoing = true;
>
> /* detect if the driver reported a value as "old frequency"
> * which is not equal to what the cpufreq core thinks is
> @@ -296,7 +296,7 @@ void __cpufreq_notify_transition(struct
> cpufreq_policy *policy,
> "No frequency transition in progress\n"))
> return;
>
> - transition_ongoing--;
> + transition_ongoing = false;
>
> adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
> pr_debug("FREQ: %lu - CPU: %lu", (unsigned long)freqs->new,
Well, now, seeing that the locking around this seems to be kind of haphazard,
I'm wondering what prevents two different threads from doing CPUFREQ_PRECHANGE
concurrently in such a way that thread A will check transition_ongoing
and thread B will check transition_ongoing and then both will set it if it
was 'false' before. And then one of them will trigger the WARN() in
CPUFREQ_POSTCHANGE.
Is there any protection in place and if so then how does it work?
Rafael
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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