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Subject[PATCH 2/2] cpufreq: stats: Fix concurrency issues while resetting stats
Date
It is possible for cpufreq_stats_clear_table() and
cpufreq_stats_record_transition() to get called concurrently and they
will try to update same variables simultaneously and may lead to
corruption of data.

Prevent that with the help of existing spinlock.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
drivers/cpufreq/cpufreq_stats.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/cpufreq_stats.c b/drivers/cpufreq/cpufreq_stats.c
index 941e63e3e652..e2db5581489a 100644
--- a/drivers/cpufreq/cpufreq_stats.c
+++ b/drivers/cpufreq/cpufreq_stats.c
@@ -31,20 +31,20 @@ static void cpufreq_stats_update(struct cpufreq_stats *stats)
{
unsigned long long cur_time = get_jiffies_64();

- spin_lock(&cpufreq_stats_lock);
stats->time_in_state[stats->last_index] += cur_time - stats->last_time;
stats->last_time = cur_time;
- spin_unlock(&cpufreq_stats_lock);
}

static void cpufreq_stats_clear_table(struct cpufreq_stats *stats)
{
unsigned int count = stats->max_state;

+ spin_lock(&cpufreq_stats_lock);
memset(stats->time_in_state, 0, count * sizeof(u64));
memset(stats->trans_table, 0, count * count * sizeof(int));
stats->last_time = get_jiffies_64();
stats->total_trans = 0;
+ spin_unlock(&cpufreq_stats_lock);
}

static ssize_t show_total_trans(struct cpufreq_policy *policy, char *buf)
@@ -62,7 +62,10 @@ static ssize_t show_time_in_state(struct cpufreq_policy *policy, char *buf)
if (policy->fast_switch_enabled)
return 0;

+ spin_lock(&cpufreq_stats_lock);
cpufreq_stats_update(stats);
+ spin_unlock(&cpufreq_stats_lock);
+
for (i = 0; i < stats->state_num; i++) {
len += sprintf(buf + len, "%u %llu\n", stats->freq_table[i],
(unsigned long long)
@@ -239,9 +242,11 @@ void cpufreq_stats_record_transition(struct cpufreq_policy *policy,
if (old_index == -1 || new_index == -1 || old_index == new_index)
return;

+ spin_lock(&cpufreq_stats_lock);
cpufreq_stats_update(stats);

stats->last_index = new_index;
stats->trans_table[old_index * stats->max_state + new_index]++;
stats->total_trans++;
+ spin_unlock(&cpufreq_stats_lock);
}
--
2.20.1.321.g9e740568ce00
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