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Commit c82e2f73 authored by Olav Haugan's avatar Olav Haugan
Browse files

core_ctl: Synchronize access to cluster cpu list 



Cluster cpu list traversal is not properly protected against removal of
element by a separate thread. Add proper locking to ensure an element
cannot be removed while accessing the list.

In addition ensure we don't end up in a livelock never exiting the loop
due to hotplug continuously moving elements to the end of the list.

Change-Id: Ie98fe48c2f4fdd0244573229b77ee9823df9e214
Signed-off-by: default avatarOlav Haugan <ohaugan@codeaurora.org>
parent e9537554

kernel/sched/core_ctl.c

+38 −0
Original line number Diff line number Diff line
@@ -719,8 +719,18 @@ static void move_cpu_lru(struct cpu_data *cpu_data) 
static void try_to_isolate(struct cluster_data *cluster, unsigned int need)

{

	struct cpu_data *c, *tmp;

	unsigned long flags;

	unsigned int num_cpus = cluster->num_cpus;



	/*

	 * Protect against entry being removed (and added at tail) by other

	 * thread (hotplug).

	 */

	spin_lock_irqsave(&state_lock, flags);

	list_for_each_entry_safe(c, tmp, &cluster->lru, sib) {

		if (!num_cpus--)

			break;



		if (!is_active(c))

			continue;

		if (cluster->active_cpus == need)
@@ -729,6 +739,8 @@ static void try_to_isolate(struct cluster_data *cluster, unsigned int need) 
		if (c->is_busy)

			continue;



		spin_unlock_irqrestore(&state_lock, flags);



		pr_debug("Trying to isolate CPU%u\n", c->cpu);

		if (!sched_isolate_cpu(c->cpu)) {

			c->isolated_by_us = true;
@@ -738,7 +750,9 @@ static void try_to_isolate(struct cluster_data *cluster, unsigned int need) 
			pr_debug("Unable to isolate CPU%u\n", c->cpu);

		}

		cluster->active_cpus = get_active_cpu_count(cluster);

		spin_lock_irqsave(&state_lock, flags);

	}

	spin_unlock_irqrestore(&state_lock, flags);



	/*

	 * If the number of active CPUs is within the limits, then
@@ -747,12 +761,19 @@ static void try_to_isolate(struct cluster_data *cluster, unsigned int need) 
	if (cluster->active_cpus <= cluster->max_cpus)

		return;



	num_cpus = cluster->num_cpus;

	spin_lock_irqsave(&state_lock, flags);

	list_for_each_entry_safe(c, tmp, &cluster->lru, sib) {

		if (!num_cpus--)

			break;



		if (!is_active(c))

			continue;

		if (cluster->active_cpus <= cluster->max_cpus)

			break;



		spin_unlock_irqrestore(&state_lock, flags);



		pr_debug("Trying to isolate CPU%u\n", c->cpu);

		if (!sched_isolate_cpu(c->cpu)) {

			c->isolated_by_us = true;
@@ -762,15 +783,28 @@ static void try_to_isolate(struct cluster_data *cluster, unsigned int need) 
			pr_debug("Unable to isolate CPU%u\n", c->cpu);

		}

		cluster->active_cpus = get_active_cpu_count(cluster);

		spin_lock_irqsave(&state_lock, flags);

	}

	spin_unlock_irqrestore(&state_lock, flags);



}



static void __try_to_unisolate(struct cluster_data *cluster,

			       unsigned int need, bool force)

{

	struct cpu_data *c, *tmp;

	unsigned long flags;

	unsigned int num_cpus = cluster->num_cpus;



	/*

	 * Protect against entry being removed (and added at tail) by other

	 * thread (hotplug).

	 */

	spin_lock_irqsave(&state_lock, flags);

	list_for_each_entry_safe(c, tmp, &cluster->lru, sib) {

		if (!num_cpus--)

			break;



		if (!c->isolated_by_us)

			continue;

		if ((c->online && !cpu_isolated(c->cpu)) ||
@@ -779,6 +813,8 @@ static void __try_to_unisolate(struct cluster_data *cluster, 
		if (cluster->active_cpus == need)

			break;



		spin_unlock_irqrestore(&state_lock, flags);



		pr_debug("Trying to unisolate CPU%u\n", c->cpu);

		if (!sched_unisolate_cpu(c->cpu)) {

			c->isolated_by_us = false;
@@ -787,7 +823,9 @@ static void __try_to_unisolate(struct cluster_data *cluster, 
			pr_debug("Unable to unisolate CPU%u\n", c->cpu);

		}

		cluster->active_cpus = get_active_cpu_count(cluster);

		spin_lock_irqsave(&state_lock, flags);

	}

	spin_unlock_irqrestore(&state_lock, flags);

}



static void try_to_unisolate(struct cluster_data *cluster, unsigned int need)