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
progress.
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: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 535dce6..e902473 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -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 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 @@
}
cs->attach_in_progress--;
-
- /*
- * 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))
- schedule_cpuset_propagate_hotplug(cs);
+ if (!cs->attach_in_progress)
+ wake_up(&cpuset_attach_wq);
mutex_unlock(&cpuset_mutex);
}
@@ -1555,10 +1552,6 @@
* 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.
*/
flush_work(&cpuset_hotplug_work);
flush_workqueue(cpuset_propagate_hotplug_wq);
@@ -2005,8 +1998,20 @@
struct cpuset *cs = container_of(work, struct cpuset, hotplug_work);
bool is_empty;
+retry:
+ wait_event(cpuset_attach_wq, cs->attach_in_progress == 0);
+
mutex_lock(&cpuset_mutex);
+ /*
+ * 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) {
+ mutex_unlock(&cpuset_mutex);
+ goto retry;
+ }
+
cpumask_andnot(&off_cpus, cs->cpus_allowed, top_cpuset.cpus_allowed);
nodes_andnot(off_mems, cs->mems_allowed, top_cpuset.mems_allowed);