From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: linaro-kernel@lists.linaro.org, patches@linaro.org,
cpufreq@vger.kernel.org, linux-pm@vger.kernel.org,
linux-kernel@vger.kernel.org, robin.randhawa@arm.com,
Steve.Bannister@arm.com, Liviu.Dudau@arm.com,
charles.garcia-tobin@arm.com, arvind.chauhan@arm.com,
dave.martin@arm.com
Subject: Re: [PATCH 13/13] cpufreq: make sure frequency transitions are serialized
Date: Wed, 26 Jun 2013 23:57:51 +0200 [thread overview]
Message-ID: <2081161.dnl1xTqcUT@vostro.rjw.lan> (raw)
In-Reply-To: <CAKohponyMG-uA93ZpH-KD+EOQPmk5tT_QoaQ7+NCEf48vYj5-w@mail.gmail.com>
On Monday, June 24, 2013 07:01:59 PM Viresh Kumar wrote:
> On 24 June 2013 19:03, Rafael J. Wysocki <rjw@sisk.pl> 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.
next prev parent reply other threads:[~2013-06-26 21:48 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-19 8:52 [PATCH 00/13] CPUFreq: Fix {PRE|POST}CHANGE notification sequence Viresh Kumar
2013-06-19 8:52 ` [PATCH 01/13] cpufreq: acpi: call CPUFREQ_POSTCHANGE notfier in error cases Viresh Kumar
2013-06-19 8:52 ` [PATCH 02/13] cpufreq: arm-big-little: " Viresh Kumar
2013-06-19 8:52 ` [PATCH 03/13] cpufreq: davinci: " Viresh Kumar
2013-06-19 8:58 ` Sekhar Nori
2013-06-19 8:52 ` [PATCH 04/13] cpufreq: dbx500: " Viresh Kumar
2013-06-19 19:42 ` Linus Walleij
2013-06-19 8:52 ` [PATCH 05/13] cpufreq: e_powersave: " Viresh Kumar
2013-06-19 12:22 ` Simon Horman
2013-06-19 14:54 ` Viresh Kumar
2013-06-19 15:08 ` Dave Jones
2013-06-19 8:53 ` [PATCH 06/13] cpufreq: exynos: " Viresh Kumar
2013-06-19 8:53 ` [PATCH 07/13] cpufreq: imx6q: " Viresh Kumar
2013-06-20 2:52 ` Shawn Guo
2013-06-19 8:53 ` [PATCH 08/13] cpufreq: omap: " Viresh Kumar
2013-06-19 14:44 ` Santosh Shilimkar
2013-06-19 8:53 ` [PATCH 09/13] cpufreq: pcc: " Viresh Kumar
2013-06-19 8:53 ` [PATCH 10/13] cpufreq: powernow-k8: " Viresh Kumar
2013-06-19 8:53 ` [PATCH 11/13] cpufreq: s3c64xx: " Viresh Kumar
2013-06-19 8:53 ` [PATCH 12/13] cpufreq: tegra: " Viresh Kumar
2013-06-19 17:11 ` Stephen Warren
2013-06-19 8:53 ` [PATCH 13/13] cpufreq: make sure frequency transitions are serialized Viresh Kumar
2013-06-24 11:43 ` Rafael J. Wysocki
2013-06-24 13:08 ` Viresh Kumar
2013-06-24 13:23 ` Rafael J. Wysocki
2013-06-24 13:16 ` Viresh Kumar
2013-06-24 13:33 ` Rafael J. Wysocki
2013-06-24 13:31 ` Viresh Kumar
2013-06-26 21:57 ` Rafael J. Wysocki [this message]
2013-06-27 4:56 ` Viresh Kumar
2013-06-27 12:15 ` Rafael J. Wysocki
2013-06-24 11:58 ` [PATCH 00/13] CPUFreq: Fix {PRE|POST}CHANGE notification sequence Rafael J. Wysocki
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