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Commit 4235053a authored by Todd Poynor's avatar Todd Poynor Committed by Amit Pundir
Browse files

cpufreq: interactive: fix racy timer stopping 



When stopping the governor, del_timer_sync() can race against an
invocation of the idle notifier callback, which has the potential
to reactivate the timer.

To fix this issue, a read-write semaphore is used. Multiple readers are
allowed as long as pcpu->governor_enabled is true.  However it can be
moved to false only after taking a write semaphore which would wait for
any on-going asynchronous activities to complete and prevent any more of
those activities to be initiated.

[toddpoynor@google.com: cosmetic and commit text changes]
Change-Id: Ib51165a735d73dcf964a06754c48bdc1913e13d0
Signed-off-by: default avatarNicolas Pitre <nicolas.pitre@linaro.org>
parent eb84e533

drivers/cpufreq/cpufreq_interactive.c

+28 −10
Original line number Diff line number Diff line
@@ -21,7 +21,7 @@ 
#include <linux/cpufreq.h>

#include <linux/module.h>

#include <linux/moduleparam.h>

#include <linux/mutex.h>

#include <linux/rwsem.h>

#include <linux/sched.h>

#include <linux/sched/rt.h>

#include <linux/tick.h>
@@ -29,7 +29,6 @@ 
#include <linux/timer.h>

#include <linux/workqueue.h>

#include <linux/kthread.h>

#include <linux/mutex.h>

#include <linux/slab.h>

#include <asm/cputime.h>
@@ -52,6 +51,7 @@ struct cpufreq_interactive_cpuinfo { 
	unsigned int floor_freq;

	u64 floor_validate_time;

	u64 hispeed_validate_time;

	struct rw_semaphore enable_sem;

	int governor_enabled;

};
@@ -279,8 +279,8 @@ static void cpufreq_interactive_timer(unsigned long data) 
	unsigned long flags;

	bool boosted;



	smp_rmb();



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

		return;

	if (!pcpu->governor_enabled)

		goto exit;
@@ -387,6 +387,7 @@ static void cpufreq_interactive_timer(unsigned long data) 
		cpufreq_interactive_timer_resched(pcpu);



exit:

	up_read(&pcpu->enable_sem);

	return;

}
@@ -396,8 +397,12 @@ static void cpufreq_interactive_idle_start(void) 
		&per_cpu(cpuinfo, smp_processor_id());

	int pending;



	if (!pcpu->governor_enabled)

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

		return;

	if (!pcpu->governor_enabled) {

		up_read(&pcpu->enable_sem);

		return;

	}



	pending = timer_pending(&pcpu->cpu_timer);
@@ -414,6 +419,7 @@ static void cpufreq_interactive_idle_start(void) 
			cpufreq_interactive_timer_resched(pcpu);

	}



	up_read(&pcpu->enable_sem);

}



static void cpufreq_interactive_idle_end(void)
@@ -421,8 +427,12 @@ static void cpufreq_interactive_idle_end(void) 
	struct cpufreq_interactive_cpuinfo *pcpu =

		&per_cpu(cpuinfo, smp_processor_id());



	if (!pcpu->governor_enabled)

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

		return;

	if (!pcpu->governor_enabled) {

		up_read(&pcpu->enable_sem);

		return;

	}



	/* Arm the timer for 1-2 ticks later if not already. */

	if (!timer_pending(&pcpu->cpu_timer)) {
@@ -432,6 +442,8 @@ static void cpufreq_interactive_idle_end(void) 
		del_timer(&pcpu->cpu_slack_timer);

		cpufreq_interactive_timer(smp_processor_id());

	}



	up_read(&pcpu->enable_sem);

}



static int cpufreq_interactive_speedchange_task(void *data)
@@ -466,10 +478,12 @@ static int cpufreq_interactive_speedchange_task(void *data) 
			unsigned int max_freq = 0;



			pcpu = &per_cpu(cpuinfo, cpu);

			smp_rmb();



			if (!pcpu->governor_enabled)

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

				continue;

			if (!pcpu->governor_enabled) {

				up_read(&pcpu->enable_sem);

				continue;

			}



			for_each_cpu(j, pcpu->policy->cpus) {

				struct cpufreq_interactive_cpuinfo *pjcpu =
@@ -486,6 +500,8 @@ static int cpufreq_interactive_speedchange_task(void *data) 
			trace_cpufreq_interactive_setspeed(cpu,

						     pcpu->target_freq,

						     pcpu->policy->cur);



			up_read(&pcpu->enable_sem);

		}

	}
@@ -936,10 +952,11 @@ static int cpufreq_governor_interactive(struct cpufreq_policy *policy, 
	case CPUFREQ_GOV_STOP:

		for_each_cpu(j, policy->cpus) {

			pcpu = &per_cpu(cpuinfo, j);

			down_write(&pcpu->enable_sem);

			pcpu->governor_enabled = 0;

			smp_wmb();

			del_timer_sync(&pcpu->cpu_timer);

			del_timer_sync(&pcpu->cpu_slack_timer);

			up_write(&pcpu->enable_sem);

		}



		if (atomic_dec_return(&active_count) > 0)
@@ -989,6 +1006,7 @@ static int __init cpufreq_interactive_init(void) 
		init_timer(&pcpu->cpu_slack_timer);

		pcpu->cpu_slack_timer.function = cpufreq_interactive_nop_timer;

		spin_lock_init(&pcpu->load_lock);

		init_rwsem(&pcpu->enable_sem);

	}



	spin_lock_init(&target_loads_lock);