workqueue: reimplement workqueue freeze using max_active
Currently, workqueue freezing is implemented by marking the worker
freezeable and calling try_to_freeze() from dispatch loop.
Reimplement it using cwq->limit so that the workqueue is frozen
instead of the worker.
* workqueue_struct->saved_max_active is added which stores the
specified max_active on initialization.
* On freeze, all cwq->max_active's are quenched to zero. Freezing is
complete when nr_active on all cwqs reach zero.
* On thaw, all cwq->max_active's are restored to wq->saved_max_active
and the worklist is repopulated.
This new implementation allows having single shared pool of workers
per cpu.
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index e541b5d..4d059c5 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -78,7 +78,7 @@
int nr_in_flight[WORK_NR_COLORS];
/* L: nr of in_flight works */
int nr_active; /* L: nr of active works */
- int max_active; /* I: max active works */
+ int max_active; /* L: max active works */
struct list_head delayed_works; /* L: delayed works */
};
@@ -108,6 +108,7 @@
struct list_head flusher_queue; /* F: flush waiters */
struct list_head flusher_overflow; /* F: flush overflow list */
+ int saved_max_active; /* I: saved cwq max_active */
const char *name; /* I: workqueue name */
#ifdef CONFIG_LOCKDEP
struct lockdep_map lockdep_map;
@@ -228,6 +229,7 @@
static DEFINE_SPINLOCK(workqueue_lock);
static LIST_HEAD(workqueues);
static DEFINE_PER_CPU(struct ida, worker_ida);
+static bool workqueue_freezing; /* W: have wqs started freezing? */
static int worker_thread(void *__worker);
@@ -745,19 +747,13 @@
struct cpu_workqueue_struct *cwq = worker->cwq;
DEFINE_WAIT(wait);
- if (cwq->wq->flags & WQ_FREEZEABLE)
- set_freezable();
-
for (;;) {
prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
- if (!freezing(current) &&
- !kthread_should_stop() &&
+ if (!kthread_should_stop() &&
list_empty(&cwq->worklist))
schedule();
finish_wait(&cwq->more_work, &wait);
- try_to_freeze();
-
if (kthread_should_stop())
break;
@@ -1553,6 +1549,7 @@
goto err;
wq->flags = flags;
+ wq->saved_max_active = max_active;
mutex_init(&wq->flush_mutex);
atomic_set(&wq->nr_cwqs_to_flush, 0);
INIT_LIST_HEAD(&wq->flusher_queue);
@@ -1591,8 +1588,19 @@
failed = true;
}
+ /*
+ * workqueue_lock protects global freeze state and workqueues
+ * list. Grab it, set max_active accordingly and add the new
+ * workqueue to workqueues list.
+ */
spin_lock(&workqueue_lock);
+
+ if (workqueue_freezing && wq->flags & WQ_FREEZEABLE)
+ for_each_possible_cpu(cpu)
+ get_cwq(cpu, wq)->max_active = 0;
+
list_add(&wq->list, &workqueues);
+
spin_unlock(&workqueue_lock);
cpu_maps_update_done();
@@ -1621,14 +1629,18 @@
{
int cpu;
+ flush_workqueue(wq);
+
+ /*
+ * wq list is used to freeze wq, remove from list after
+ * flushing is complete in case freeze races us.
+ */
cpu_maps_update_begin();
spin_lock(&workqueue_lock);
list_del(&wq->list);
spin_unlock(&workqueue_lock);
cpu_maps_update_done();
- flush_workqueue(wq);
-
for_each_possible_cpu(cpu) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
int i;
@@ -1722,6 +1734,137 @@
EXPORT_SYMBOL_GPL(work_on_cpu);
#endif /* CONFIG_SMP */
+#ifdef CONFIG_FREEZER
+
+/**
+ * freeze_workqueues_begin - begin freezing workqueues
+ *
+ * Start freezing workqueues. After this function returns, all
+ * freezeable workqueues will queue new works to their frozen_works
+ * list instead of the cwq ones.
+ *
+ * CONTEXT:
+ * Grabs and releases workqueue_lock and cwq->lock's.
+ */
+void freeze_workqueues_begin(void)
+{
+ struct workqueue_struct *wq;
+ unsigned int cpu;
+
+ spin_lock(&workqueue_lock);
+
+ BUG_ON(workqueue_freezing);
+ workqueue_freezing = true;
+
+ for_each_possible_cpu(cpu) {
+ list_for_each_entry(wq, &workqueues, list) {
+ struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
+
+ spin_lock_irq(&cwq->lock);
+
+ if (wq->flags & WQ_FREEZEABLE)
+ cwq->max_active = 0;
+
+ spin_unlock_irq(&cwq->lock);
+ }
+ }
+
+ spin_unlock(&workqueue_lock);
+}
+
+/**
+ * freeze_workqueues_busy - are freezeable workqueues still busy?
+ *
+ * Check whether freezing is complete. This function must be called
+ * between freeze_workqueues_begin() and thaw_workqueues().
+ *
+ * CONTEXT:
+ * Grabs and releases workqueue_lock.
+ *
+ * RETURNS:
+ * %true if some freezeable workqueues are still busy. %false if
+ * freezing is complete.
+ */
+bool freeze_workqueues_busy(void)
+{
+ struct workqueue_struct *wq;
+ unsigned int cpu;
+ bool busy = false;
+
+ spin_lock(&workqueue_lock);
+
+ BUG_ON(!workqueue_freezing);
+
+ for_each_possible_cpu(cpu) {
+ /*
+ * nr_active is monotonically decreasing. It's safe
+ * to peek without lock.
+ */
+ list_for_each_entry(wq, &workqueues, list) {
+ struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
+
+ if (!(wq->flags & WQ_FREEZEABLE))
+ continue;
+
+ BUG_ON(cwq->nr_active < 0);
+ if (cwq->nr_active) {
+ busy = true;
+ goto out_unlock;
+ }
+ }
+ }
+out_unlock:
+ spin_unlock(&workqueue_lock);
+ return busy;
+}
+
+/**
+ * thaw_workqueues - thaw workqueues
+ *
+ * Thaw workqueues. Normal queueing is restored and all collected
+ * frozen works are transferred to their respective cwq worklists.
+ *
+ * CONTEXT:
+ * Grabs and releases workqueue_lock and cwq->lock's.
+ */
+void thaw_workqueues(void)
+{
+ struct workqueue_struct *wq;
+ unsigned int cpu;
+
+ spin_lock(&workqueue_lock);
+
+ if (!workqueue_freezing)
+ goto out_unlock;
+
+ for_each_possible_cpu(cpu) {
+ list_for_each_entry(wq, &workqueues, list) {
+ struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
+
+ if (!(wq->flags & WQ_FREEZEABLE))
+ continue;
+
+ spin_lock_irq(&cwq->lock);
+
+ /* restore max_active and repopulate worklist */
+ cwq->max_active = wq->saved_max_active;
+
+ while (!list_empty(&cwq->delayed_works) &&
+ cwq->nr_active < cwq->max_active)
+ cwq_activate_first_delayed(cwq);
+
+ wake_up(&cwq->more_work);
+
+ spin_unlock_irq(&cwq->lock);
+ }
+ }
+
+ workqueue_freezing = false;
+out_unlock:
+ spin_unlock(&workqueue_lock);
+}
+#endif /* CONFIG_FREEZER */
+
void __init init_workqueues(void)
{
unsigned int cpu;