cpuset_hotplug_workfn() has been invoking cpuset_propagate_hotplug()
directly to propagate hotplug updates to !root cpusets; however, this
has the following problems.
* cpuset locking is scheduled to be decoupled from cgroup_mutex,
cgroup_mutex will be unexported, and cgroup_attach_task() will do
cgroup locking internally, so propagation can't synchronously move
tasks to a parent cgroup while walking the hierarchy.
* We can't use cgroup generic tree iterator because propagation to
each cpuset may sleep. With propagation done asynchronously, we can
lose the rather ugly cpuset specific iteration.
Convert cpuset_propagate_hotplug() to
cpuset_propagate_hotplug_workfn() and execute it from newly added
cpuset->hotplug_work. The work items are run on an ordered workqueue,
so the propagation order is preserved. cpuset_hotplug_workfn()
schedules all propagations while holding cgroup_mutex and waits for
completion without cgroup_mutex. Each in-flight propagation holds a
reference to the cpuset->css.
This patch doesn't cause any functional difference.
Signed-off-by: Tejun Heo <t...@kernel.org>
---
kernel/cpuset.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 48 insertions(+), 6 deletions(-)
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 74e412f..2d0b9bc 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -99,6 +99,8 @@ struct cpuset {
/* used for walking a cpuset hierarchy */
struct list_head stack_list;
+
+ struct work_struct hotplug_work;
};
/* Retrieve the cpuset for a cgroup */
@@ -254,7 +256,10 @@ static DEFINE_SPINLOCK(cpuset_buffer_lock);
/*
* CPU / memory hotplug is handled asynchronously.
*/
+static struct workqueue_struct *cpuset_propagate_hotplug_wq;
+
static void cpuset_hotplug_workfn(struct work_struct *work);
+static void cpuset_propagate_hotplug_workfn(struct work_struct *work);
static DECLARE_WORK(cpuset_hotplug_work, cpuset_hotplug_workfn);
@@ -1808,6 +1813,7 @@ static struct cgroup_subsys_state
*cpuset_css_alloc(struct cgroup *cont)
cpumask_clear(cs->cpus_allowed);
nodes_clear(cs->mems_allowed);
fmeter_init(&cs->fmeter);
+ INIT_WORK(&cs->hotplug_work, cpuset_propagate_hotplug_workfn);
cs->relax_domain_level = -1;
cs->parent = cgroup_cs(cont->parent);
@@ -2033,21 +2039,20 @@ static struct cpuset *cpuset_next(struct list_head
*queue)
}
/**
- * cpuset_propagate_hotplug - propagate CPU/memory hotplug to a cpuset
+ * cpuset_propagate_hotplug_workfn - propagate CPU/memory hotplug to a cpuset
* @cs: cpuset in interest
*
* Compare @cs's cpu and mem masks against top_cpuset and if some have gone
* offline, update @cs accordingly. If @cs ends up with no CPU or memory,
* all its tasks are moved to the nearest ancestor with both resources.
- *
- * Should be called with cgroup_mutex held.
*/
-static void cpuset_propagate_hotplug(struct cpuset *cs)
+static void cpuset_propagate_hotplug_workfn(struct work_struct *work)
{
static cpumask_t off_cpus;
static nodemask_t off_mems, tmp_mems;
+ struct cpuset *cs = container_of(work, struct cpuset, hotplug_work);
- WARN_ON_ONCE(!cgroup_lock_is_held());
+ cgroup_lock();
cpumask_andnot(&off_cpus, cs->cpus_allowed, top_cpuset.cpus_allowed);
nodes_andnot(off_mems, cs->mems_allowed, top_cpuset.mems_allowed);
@@ -2071,6 +2076,36 @@ static void cpuset_propagate_hotplug(struct cpuset *cs)
if (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
remove_tasks_in_empty_cpuset(cs);
+
+ cgroup_unlock();
+
+ /* the following may free @cs, should be the last operation */
+ css_put(&cs->css);
+}
+
+/**
+ * schedule_cpuset_propagate_hotplug - schedule hotplug propagation to a cpuset
+ * @cs: cpuset of interest
+ *
+ * Schedule cpuset_propagate_hotplug_workfn() which will update CPU and
+ * memory masks according to top_cpuset.
+ */
+static void schedule_cpuset_propagate_hotplug(struct cpuset *cs)
+{
+ /*
+ * Pin @cs. The refcnt will be released when the work item
+ * finishes executing.
+ */
+ if (!css_tryget(&cs->css))
+ return;
+
+ /*
+ * Queue @cs->empty_cpuset_work. If already pending, lose the css
+ * ref. cpuset_propagate_hotplug_wq is ordered and propagation
+ * will happen in the order this function is called.
+ */
+ if (!queue_work(cpuset_propagate_hotplug_wq, &cs->hotplug_work))
+ css_put(&cs->css);
}
/**
@@ -2135,11 +2170,14 @@ static void cpuset_hotplug_workfn(struct work_struct
*work)
list_add_tail(&top_cpuset.stack_list, &queue);
while ((cs = cpuset_next(&queue)))
if (cs != &top_cpuset)
- cpuset_propagate_hotplug(cs);
+ schedule_cpuset_propagate_hotplug(cs);
}
cgroup_unlock();
+ /* wait for propagations to finish */
+ flush_workqueue(cpuset_propagate_hotplug_wq);
+
/* rebuild sched domains if cpus_allowed has changed */
if (cpus_updated) {
struct sched_domain_attr *attr;
@@ -2196,6 +2234,10 @@ void __init cpuset_init_smp(void)
top_cpuset.mems_allowed = node_states[N_MEMORY];
hotplug_memory_notifier(cpuset_track_online_nodes, 10);
+
+ cpuset_propagate_hotplug_wq =
+ alloc_ordered_workqueue("cpuset_hotplug", 0);
+ BUG_ON(!cpuset_propagate_hotplug_wq);
}
/**
--
1.8.0.2
--
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