Commit e44193d3 authored by Li Zefan's avatar Li Zefan Committed by Tejun Heo

cpuset: let hotplug propagation work wait for task attaching

Instead of triggering propagation work in cpuset_attach(), we make
hotplug propagation work wait until there's no task attaching in

IMO this is more robust. We won't see empty masks in cpuset_attach().

Also it's a preparation for removing propagation work. Without asynchronous
propagation we can't call move_tasks_in_empty_cpuset() in cpuset_attach(),
because otherwise we'll deadlock on cgroup_mutex.

tj: typo fixes.
Signed-off-by: default avatarLi Zefan <>
Signed-off-by: default avatarTejun Heo <>
parent a73456f3
......@@ -59,6 +59,7 @@
#include <linux/mutex.h>
#include <linux/workqueue.h>
#include <linux/cgroup.h>
#include <linux/wait.h>
* Tracks how many cpusets are currently defined in system.
......@@ -275,6 +276,8 @@ static void schedule_cpuset_propagate_hotplug(struct cpuset *cs);
static DECLARE_WORK(cpuset_hotplug_work, cpuset_hotplug_workfn);
static DECLARE_WAIT_QUEUE_HEAD(cpuset_attach_wq);
* This is ugly, but preserves the userspace API for existing cpuset
* users. If someone tries to mount the "cpuset" filesystem, we
......@@ -1436,14 +1439,8 @@ static void cpuset_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
* We may have raced with CPU/memory hotunplug. Trigger hotplug
* propagation if @cs doesn't have any CPU or memory. It will move
* the newly added tasks to the nearest parent which can execute.
if (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
if (!cs->attach_in_progress)
......@@ -1555,10 +1552,6 @@ static int cpuset_write_resmask(struct cgroup *cgrp, struct cftype *cft,
* resources, wait for the previously scheduled operations before
* proceeding, so that we don't end up keep removing tasks added
* after execution capability is restored.
* Flushing cpuset_hotplug_work is enough to synchronize against
* hotplug hanlding; however, cpuset_attach() may schedule
* propagation work directly. Flush the workqueue too.
......@@ -2005,8 +1998,20 @@ static void cpuset_propagate_hotplug_workfn(struct work_struct *work)
struct cpuset *cs = container_of(work, struct cpuset, hotplug_work);
bool is_empty;
wait_event(cpuset_attach_wq, cs->attach_in_progress == 0);
* We have raced with task attaching. We wait until attaching
* is finished, so we won't attach a task to an empty cpuset.
if (cs->attach_in_progress) {
goto retry;
cpumask_andnot(&off_cpus, cs->cpus_allowed, top_cpuset.cpus_allowed);
nodes_andnot(off_mems, cs->mems_allowed, top_cpuset.mems_allowed);
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