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.ku...@linaro.org>
---
drivers/cpufreq/cpufreq.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 2d53f47..92cb8b3 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 int transition_ongoing;
+
static bool init_cpufreq_transition_notifier_list_called;
static int __init init_cpufreq_transition_notifier_list(void)
{
@@ -264,6 +267,8 @@ void __cpufreq_notify_transition(struct cpufreq_policy
*policy,
switch (state) {
case CPUFREQ_PRECHANGE:
+ WARN_ON(transition_ongoing++);
+
/* 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 +288,8 @@ void __cpufreq_notify_transition(struct cpufreq_policy
*policy,
break;
case CPUFREQ_POSTCHANGE:
+ WARN_ON(!transition_ongoing--);
+
adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
pr_debug("FREQ: %lu - CPU: %lu", (unsigned long)freqs->new,
(unsigned long)freqs->cpu);
@@ -1458,6 +1465,8 @@ 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
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