Re: [PATCH 13/13] cpufreq: make sure frequency transitions are serialized

[Viresh Kumar <viresh.kumar@linaro.org>]

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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,

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From b8c3bd9fcb521f1b66d52f157fc26eccf6cc4f29 Mon Sep 17 00:00:00 2001
Message-Id: <b8c3bd9fcb521f1b66d52f157fc26eccf6cc4f29.1372080656.git.viresh.kumar@linaro.org>
From: Viresh Kumar <viresh.kumar@linaro.org>
Date: Wed, 19 Jun 2013 10:16:55 +0530
Subject: [PATCH] cpufreq: make sure frequency transitions are serialized

Whenever we are changing frequency of a cpu, we are calling PRECHANGE and
POSTCHANGE notifiers. They must be serialized. i.e. PRECHANGE or POSTCHANGE
shouldn't be called twice contiguously.

This can happen due to bugs in users of __cpufreq_driver_target() or actual
cpufreq drivers who are sending these notifiers.

This patch adds some protection against this. Now, we keep track of the last
transaction and see if something went wrong.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 drivers/cpufreq/cpufreq.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 2d53f47..49d942a 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -107,6 +107,9 @@ static void handle_update(struct work_struct *work);
 static BLOCKING_NOTIFIER_HEAD(cpufreq_policy_notifier_list);
 static struct srcu_notifier_head cpufreq_transition_notifier_list;
 
+/* Tracks status of transition */
+static bool transition_ongoing;
+
 static bool init_cpufreq_transition_notifier_list_called;
 static int __init init_cpufreq_transition_notifier_list(void)
 {
@@ -264,6 +267,12 @@ void __cpufreq_notify_transition(struct cpufreq_policy *policy,
 	switch (state) {
 
 	case CPUFREQ_PRECHANGE:
+		if (WARN(transition_ongoing,
+				"In middle of another frequency transition\n"))
+			return;
+
+		transition_ongoing = true;
+
 		/* detect if the driver reported a value as "old frequency"
 		 * which is not equal to what the cpufreq core thinks is
 		 * "old frequency".
@@ -283,6 +292,12 @@ void __cpufreq_notify_transition(struct cpufreq_policy *policy,
 		break;
 
 	case CPUFREQ_POSTCHANGE:
+		if (WARN(!transition_ongoing,
+				"No frequency transition in progress\n"))
+			return;
+
+		transition_ongoing = false;
+
 		adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
 		pr_debug("FREQ: %lu - CPU: %lu", (unsigned long)freqs->new,
 			(unsigned long)freqs->cpu);
@@ -1458,6 +1473,8 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy,
 
 	if (cpufreq_disabled())
 		return -ENODEV;
+	if (transition_ongoing)
+		return -EBUSY;
 
 	/* Make sure that target_freq is within supported range */
 	if (target_freq > policy->max)
-- 
1.7.12.rc2.18.g61b472e