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Commit 927d2c14 authored by Pavankumar Kondeti's avatar Pavankumar Kondeti
Browse files

sched: Fix deadlock between cpu hotplug and upmigrate change 



There is a circular dependency between cpu_hotplug.lock and
HMP scheduler policy mutex. Prevent this by enforcing the
same lock order.

Here CPU0 and CPU2 are governed by different cpufreq policies.

----------------                        --------------------
    CPU 0                                          CPU 2
---------------                         --------------------

proc_sys_call_handler()                 cpu_up()

                                        --> acquired cpu_hotplug.lock

sched_hmp_proc_update_handler()         cpufreq_cpu_callback()

--> acquired policy_mutex

                                        cpufreq_governor_interactive()

get_online_cpus()                       sched_set_window()

--> waiting for cpu_hotplug.lock        --> waiting for policy_mutex

Change-Id: I39efc394f4f00815b72adc975021fdb16fe6e30a
Signed-off-by: default avatarPavankumar Kondeti <pkondeti@codeaurora.org>
parent 0112f3c5

kernel/sched/fair.c

+20 −9
Original line number Diff line number Diff line
@@ -3805,7 +3805,21 @@ int sched_hmp_proc_update_handler(struct ctl_table *table, int write, 
	int ret;

	unsigned int old_val;

	unsigned int *data = (unsigned int *)table->data;

	int update_min_nice = 0;

	int update_task_count = 0;



	if (!sched_enable_hmp)

		return 0;



	/*

	 * The policy mutex is acquired with cpu_hotplug.lock

	 * held from cpu_up()->cpufreq_governor_interactive()->

	 * sched_set_window(). So enforce the same order here.

	 */

	if (write && (data == &sysctl_sched_upmigrate_pct ||

	    data == (unsigned int *)&sysctl_sched_upmigrate_min_nice)) {

		update_task_count = 1;

		get_online_cpus();

	}



	mutex_lock(&policy_mutex);
@@ -3813,7 +3827,7 @@ int sched_hmp_proc_update_handler(struct ctl_table *table, int write, 


	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);



	if (ret || !write || !sched_enable_hmp)

	if (ret || !write)

		goto done;



	if (write && (old_val == *data))
@@ -3828,7 +3842,6 @@ int sched_hmp_proc_update_handler(struct ctl_table *table, int write, 
			ret = -EINVAL;

			goto done;

		}

		update_min_nice = 1;

	} else if (data != &sysctl_sched_select_prev_cpu_us) {

		/*

		 * all tunables other than min_nice and prev_cpu_us are
@@ -3850,19 +3863,17 @@ int sched_hmp_proc_update_handler(struct ctl_table *table, int write, 
	 * includes taking runqueue lock of all online cpus and re-initiatizing

	 * their big counter values based on changed criteria.

	 */

	if ((data == &sysctl_sched_upmigrate_pct || update_min_nice)) {

		get_online_cpus();

	if (update_task_count)

		pre_big_task_count_change(cpu_online_mask);

	}



	set_hmp_defaults();



	if ((data == &sysctl_sched_upmigrate_pct || update_min_nice)) {

	if (update_task_count)

		post_big_task_count_change(cpu_online_mask);

		put_online_cpus();

	}



done:

	if (update_task_count)

		put_online_cpus();

	mutex_unlock(&policy_mutex);

	return ret;

}

kernel/sched/qhmp_fair.c

+20 −10
Original line number Diff line number Diff line
@@ -3883,7 +3883,22 @@ int sched_hmp_proc_update_handler(struct ctl_table *table, int write, 
	int ret;

	unsigned int old_val;

	unsigned int *data = (unsigned int *)table->data;

	int update_min_nice = 0;

	int update_task_count = 0;



	if (!sched_enable_hmp)

		return 0;



	/*

	 * The policy mutex is acquired with cpu_hotplug.lock

	 * held from cpu_up()->cpufreq_governor_interactive()->

	 * sched_set_window(). So enforce the same order here.

	 */

	if (write && (data == &sysctl_sched_upmigrate_pct ||

	    data == &sysctl_sched_small_task_pct ||

	    data == (unsigned int *)&sysctl_sched_upmigrate_min_nice)) {

		update_task_count = 1;

		get_online_cpus();

	}



	mutex_lock(&policy_mutex);
@@ -3908,7 +3923,6 @@ int sched_hmp_proc_update_handler(struct ctl_table *table, int write, 
			ret = -EINVAL;

			goto done;

		}

		update_min_nice = 1;

	} else {

		/* all tunables other than min_nice are in percentage */

		if (sysctl_sched_downmigrate_pct >
@@ -3927,21 +3941,17 @@ int sched_hmp_proc_update_handler(struct ctl_table *table, int write, 
	 * includes taking runqueue lock of all online cpus and re-initiatizing

	 * their big/small counter values based on changed criteria.

	 */

	if ((data == &sysctl_sched_upmigrate_pct ||

	     data == &sysctl_sched_small_task_pct || update_min_nice)) {

		get_online_cpus();

	if (update_task_count)

		pre_big_small_task_count_change(cpu_online_mask);

	}



	set_hmp_defaults();



	if ((data == &sysctl_sched_upmigrate_pct ||

	     data == &sysctl_sched_small_task_pct || update_min_nice)) {

	if (update_task_count)

		post_big_small_task_count_change(cpu_online_mask);

		put_online_cpus();

	}



done:

	if (update_task_count)

		put_online_cpus();

	mutex_unlock(&policy_mutex);

	return ret;

}