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Subject[PATCH 05/13] cpuset: introduce cpuset_for_each_child()
Date
Instead of iterating cgroup->children directly, introduce and use
cpuset_for_each_child() which wraps cgroup_for_each_child() and
performs online check. As it uses the generic iterator, it requires
RCU read locking too.

As cpuset is currently protected by cgroup_mutex, non-online cpusets
aren't visible to all the iterations and this patch currently doesn't
make any functional difference. This will be used to de-couple cpuset
locking from cgroup core.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/cpuset.c | 85 ++++++++++++++++++++++++++++++++++++---------------------
1 file changed, 54 insertions(+), 31 deletions(-)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 22b521d..5a52ed6 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -200,6 +200,19 @@ static struct cpuset top_cpuset = {
(1 << CS_MEM_EXCLUSIVE)),
};

+/**
+ * cpuset_for_each_child - traverse online children of a cpuset
+ * @child_cs: loop cursor pointing to the current child
+ * @pos_cgrp: used for iteration
+ * @parent_cs: target cpuset to walk children of
+ *
+ * Walk @child_cs through the online children of @parent_cs. Must be used
+ * with RCU read locked.
+ */
+#define cpuset_for_each_child(child_cs, pos_cgrp, parent_cs) \
+ cgroup_for_each_child((pos_cgrp), (parent_cs)->css.cgroup) \
+ if (is_cpuset_online(((child_cs) = cgroup_cs((pos_cgrp)))))
+
/*
* There are two global mutexes guarding cpuset structures. The first
* is the main control groups cgroup_mutex, accessed via
@@ -419,48 +432,55 @@ static int validate_change(const struct cpuset *cur, const struct cpuset *trial)
{
struct cgroup *cont;
struct cpuset *c, *par;
+ int ret;
+
+ rcu_read_lock();

/* Each of our child cpusets must be a subset of us */
- list_for_each_entry(cont, &cur->css.cgroup->children, sibling) {
- if (!is_cpuset_subset(cgroup_cs(cont), trial))
- return -EBUSY;
- }
+ ret = -EBUSY;
+ cpuset_for_each_child(c, cont, cur)
+ if (!is_cpuset_subset(c, trial))
+ goto out;

/* Remaining checks don't apply to root cpuset */
+ ret = 0;
if (cur == &top_cpuset)
- return 0;
+ goto out;

par = cur->parent;

/* We must be a subset of our parent cpuset */
+ ret = -EACCES;
if (!is_cpuset_subset(trial, par))
- return -EACCES;
+ goto out;

/*
* If either I or some sibling (!= me) is exclusive, we can't
* overlap
*/
- list_for_each_entry(cont, &par->css.cgroup->children, sibling) {
- c = cgroup_cs(cont);
+ ret = -EINVAL;
+ cpuset_for_each_child(c, cont, par) {
if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
c != cur &&
cpumask_intersects(trial->cpus_allowed, c->cpus_allowed))
- return -EINVAL;
+ goto out;
if ((is_mem_exclusive(trial) || is_mem_exclusive(c)) &&
c != cur &&
nodes_intersects(trial->mems_allowed, c->mems_allowed))
- return -EINVAL;
+ goto out;
}

/* Cpusets with tasks can't have empty cpus_allowed or mems_allowed */
- if (cgroup_task_count(cur->css.cgroup)) {
- if (cpumask_empty(trial->cpus_allowed) ||
- nodes_empty(trial->mems_allowed)) {
- return -ENOSPC;
- }
- }
+ ret = -ENOSPC;
+ if (cgroup_task_count(cur->css.cgroup) &&
+ (cpumask_empty(trial->cpus_allowed) ||
+ nodes_empty(trial->mems_allowed)))
+ goto out;

- return 0;
+ ret = 0;
+out:
+ rcu_read_unlock();
+ return ret;
}

#ifdef CONFIG_SMP
@@ -501,10 +521,10 @@ update_domain_attr_tree(struct sched_domain_attr *dattr, struct cpuset *c)
if (is_sched_load_balance(cp))
update_domain_attr(dattr, cp);

- list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
- child = cgroup_cs(cont);
+ rcu_read_lock();
+ cpuset_for_each_child(child, cont, cp)
list_add_tail(&child->stack_list, &q);
- }
+ rcu_read_unlock();
}
}

@@ -623,10 +643,10 @@ static int generate_sched_domains(cpumask_var_t **domains,
continue;
}

- list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
- child = cgroup_cs(cont);
+ rcu_read_lock();
+ cpuset_for_each_child(child, cont, cp)
list_add_tail(&child->stack_list, &q);
- }
+ rcu_read_unlock();
}

for (i = 0; i < csn; i++)
@@ -1824,7 +1844,8 @@ static int cpuset_css_online(struct cgroup *cgrp)
{
struct cpuset *cs = cgroup_cs(cgrp);
struct cpuset *parent = cs->parent;
- struct cgroup *tmp_cg;
+ struct cpuset *tmp_cs;
+ struct cgroup *pos_cg;

if (!parent)
return 0;
@@ -1853,12 +1874,14 @@ static int cpuset_css_online(struct cgroup *cgrp)
* changed to grant parent->cpus_allowed-sibling_cpus_exclusive
* (and likewise for mems) to the new cgroup.
*/
- list_for_each_entry(tmp_cg, &cgrp->parent->children, sibling) {
- struct cpuset *tmp_cs = cgroup_cs(tmp_cg);
-
- if (is_mem_exclusive(tmp_cs) || is_cpu_exclusive(tmp_cs))
+ rcu_read_lock();
+ cpuset_for_each_child(tmp_cs, pos_cg, parent) {
+ if (is_mem_exclusive(tmp_cs) || is_cpu_exclusive(tmp_cs)) {
+ rcu_read_unlock();
return 0;
+ }
}
+ rcu_read_unlock();

mutex_lock(&callback_mutex);
cs->mems_allowed = parent->mems_allowed;
@@ -2027,10 +2050,10 @@ static struct cpuset *cpuset_next(struct list_head *queue)

cp = list_first_entry(queue, struct cpuset, stack_list);
list_del(queue->next);
- list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
- child = cgroup_cs(cont);
+ rcu_read_lock();
+ cpuset_for_each_child(child, cont, cp)
list_add_tail(&child->stack_list, queue);
- }
+ rcu_read_unlock();

return cp;
}
--
1.7.11.7


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