Re: [PATCH 2/2] cpufreq: stats: Fix concurrency issues while resetting stats

From: Matthias Kaehlcke
Date: Mon Feb 04 2019 - 17:31:36 EST


On Fri, Feb 01, 2019 at 11:45:45AM +0530, Viresh Kumar wrote:
> 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@xxxxxxxxxx>
> ---
> 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);
> }

Reviewed-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>