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Subject[PATCH v14 06/12] cpuset: Track cpusets that use parent's effective_cpus
Date
In the default hierarchy, a cpuset will use the parent's effective_cpus
if none of the requested CPUs can be granted from the parent. That can
be a problem if a parent is a partition root with children partition
roots. Changes to a parent's effective_cpus list due to changes in a
child partition root may not be properly reflected in a child cpuset
that use parent's effective_cpus because the cpu_exclusive rule of a
partition root will not guard against that.

In order to avoid the mismatch, two new tracking variables are added to
the cpuset structure to track if a cpuset uses parent's effective_cpus
and the number of children cpusets that use its effective_cpus. So
whenever cpumask changes are made to a parent, it will also check to
see if it has other children cpusets that use its effective_cpus and
call update_cpumasks_hier() if that is the case.

Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/cgroup/cpuset.c | 71 +++++++++++++++++++++++++++++++++++++++++-
1 file changed, 70 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index a1f6fdb6be02..596e0b16fb96 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -147,6 +147,14 @@ struct cpuset {

/* partition root state */
int partition_root_state;
+
+ /*
+ * Default hierarchy only:
+ * use_parent_ecpus - set if using parent's effective_cpus
+ * child_ecpus_count - # of children with use_parent_ecpus set
+ */
+ int use_parent_ecpus;
+ int child_ecpus_count;
};

/*
@@ -1227,8 +1235,17 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp)
* If it becomes empty, inherit the effective mask of the
* parent, which is guaranteed to have some CPUs.
*/
- if (is_in_v2_mode() && cpumask_empty(tmp->new_cpus))
+ if (is_in_v2_mode() && cpumask_empty(tmp->new_cpus)) {
cpumask_copy(tmp->new_cpus, parent->effective_cpus);
+ if (!cp->use_parent_ecpus) {
+ cp->use_parent_ecpus = true;
+ parent->child_ecpus_count++;
+ }
+ } else if (cp->use_parent_ecpus) {
+ cp->use_parent_ecpus = false;
+ WARN_ON_ONCE(!parent->child_ecpus_count);
+ parent->child_ecpus_count--;
+ }

/*
* Skip the whole subtree if the cpumask remains the same
@@ -1340,6 +1357,35 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp)
rebuild_sched_domains_locked();
}

+/**
+ * update_sibling_cpumasks - Update siblings cpumasks
+ * @parent: Parent cpuset
+ * @cs: Current cpuset
+ * @tmp: Temp variables
+ */
+static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
+ struct tmpmasks *tmp)
+{
+ struct cpuset *sibling;
+ struct cgroup_subsys_state *pos_css;
+
+ /*
+ * Check all its siblings and call update_cpumasks_hier()
+ * if their use_parent_ecpus flag is set in order for them
+ * to use the right effective_cpus value.
+ */
+ rcu_read_lock();
+ cpuset_for_each_child(sibling, pos_css, parent) {
+ if (sibling == cs)
+ continue;
+ if (!sibling->use_parent_ecpus)
+ continue;
+
+ update_cpumasks_hier(sibling, tmp);
+ }
+ rcu_read_unlock();
+}
+
/**
* update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
* @cs: the cpuset to consider
@@ -1415,6 +1461,17 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
spin_unlock_irq(&callback_lock);

update_cpumasks_hier(cs, &tmp);
+
+ if (cs->partition_root_state) {
+ struct cpuset *parent = parent_cs(cs);
+
+ /*
+ * For partition root, update the cpumasks of sibling
+ * cpusets if they use parent's effective_cpus.
+ */
+ if (parent->child_ecpus_count)
+ update_sibling_cpumasks(parent, cs, &tmp);
+ }
return 0;
}

@@ -1851,6 +1908,9 @@ static int update_prstate(struct cpuset *cs, int val)
if (parent != &top_cpuset)
update_tasks_cpumask(parent);

+ if (parent->child_ecpus_count)
+ update_sibling_cpumasks(parent, cs, &tmp);
+
rebuild_sched_domains_locked();
out:
free_cpumasks(NULL, &tmp);
@@ -2545,6 +2605,8 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
if (is_in_v2_mode()) {
cpumask_copy(cs->effective_cpus, parent->effective_cpus);
cs->effective_mems = parent->effective_mems;
+ cs->use_parent_ecpus = true;
+ parent->child_ecpus_count++;
}
spin_unlock_irq(&callback_lock);

@@ -2608,6 +2670,13 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
is_sched_load_balance(cs))
update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);

+ if (cs->use_parent_ecpus) {
+ struct cpuset *parent = parent_cs(cs);
+
+ cs->use_parent_ecpus = false;
+ parent->child_ecpus_count--;
+ }
+
cpuset_dec();
clear_bit(CS_ONLINE, &cs->flags);

--
2.18.0
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