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Commit 5b10bb9f authored by Junjie Wu's avatar Junjie Wu Committed by Matt Wagantall
Browse files

cpufreq: interactive: Avoid down_read_trylock if down_write() is held 



down_read_trylock is not always non-blocking if the same thread calls
down_write() before.

CPU1					CPU2
					down_read()
down_write()
  __down_write_nested()
    schedule()
      __down_read_trylock()
					up_read()
					  acquires sem->wait_lock
					    __rwsem_wake_one_writer()
	tries to lock sem->wait_lock

Now CPU2 is waiting for CPU1's schedule() to complete, while holding
sem->wait_lock. CPU1 needs sem->wait_lock to continue.

This problem only happens after cpufreq_interactive introduced load
change notification that could be called within schedule().

Add a separate flag to ignore notification if current thread is in
middle of down_write(). This avoids attempting to hold sem->wait_lock.
The additional flag doesn't have any side effects because
down_read_trylock() would have failed anyway.

Change-Id: Iff97cac36c170cf6d03f36de695141289c3d6930
Signed-off-by: default avatarJunjie Wu <junjiew@codeaurora.org>
parent 5920d95f

drivers/cpufreq/cpufreq_interactive.c

+10 −0
Original line number Diff line number Diff line
@@ -54,6 +54,7 @@ struct cpufreq_interactive_cpuinfo { 
	u64 local_hvtime; /* per-cpu hispeed_validate_time */

	u64 max_freq_idle_start_time;

	struct rw_semaphore enable_sem;

	bool reject_notification;

	int governor_enabled;

	struct cpufreq_interactive_tunables *cached_tunables;

	int first_cpu;
@@ -758,6 +759,9 @@ static int load_change_callback(struct notifier_block *nb, unsigned long val, 
	if (speedchange_task == current)

		return 0;



	if (pcpu->reject_notification)

		return 0;



	if (!down_read_trylock(&pcpu->enable_sem))

		return 0;

	if (!pcpu->governor_enabled) {
@@ -1657,6 +1661,7 @@ static int cpufreq_governor_interactive(struct cpufreq_policy *policy, 
				pcpu->floor_validate_time;

			pcpu->local_hvtime = pcpu->floor_validate_time;

			pcpu->max_freq = policy->max;

			pcpu->reject_notification = true;

			down_write(&pcpu->enable_sem);

			del_timer_sync(&pcpu->cpu_timer);

			del_timer_sync(&pcpu->cpu_slack_timer);
@@ -1664,6 +1669,7 @@ static int cpufreq_governor_interactive(struct cpufreq_policy *policy, 
			cpufreq_interactive_timer_start(tunables, j);

			pcpu->governor_enabled = 1;

			up_write(&pcpu->enable_sem);

			pcpu->reject_notification = false;

		}



		mutex_unlock(&gov_lock);
@@ -1673,11 +1679,13 @@ static int cpufreq_governor_interactive(struct cpufreq_policy *policy, 
		mutex_lock(&gov_lock);

		for_each_cpu(j, policy->cpus) {

			pcpu = &per_cpu(cpuinfo, j);

			pcpu->reject_notification = true;

			down_write(&pcpu->enable_sem);

			pcpu->governor_enabled = 0;

			del_timer_sync(&pcpu->cpu_timer);

			del_timer_sync(&pcpu->cpu_slack_timer);

			up_write(&pcpu->enable_sem);

			pcpu->reject_notification = false;

		}



		mutex_unlock(&gov_lock);
@@ -1716,11 +1724,13 @@ static int cpufreq_governor_interactive(struct cpufreq_policy *policy, 
			 */



			if (policy->max > pcpu->max_freq) {

				pcpu->reject_notification = true;

				down_write(&pcpu->enable_sem);

				del_timer_sync(&pcpu->cpu_timer);

				del_timer_sync(&pcpu->cpu_slack_timer);

				cpufreq_interactive_timer_resched(j);

				up_write(&pcpu->enable_sem);

				pcpu->reject_notification = false;

			}



			pcpu->max_freq = policy->max;