workqueue: separate out drain_workqueue() from destroy_workqueue()
There are users which want to drain workqueues without destroying it.
Separate out drain functionality from destroy_workqueue() into
drain_workqueue() and make it accessible to workqueue users.
To guarantee forward-progress, only chain queueing is allowed while
drain is in progress. If a new work item which isn't chained from the
running or pending work items is queued while draining is in progress,
WARN_ON_ONCE() is triggered.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index e3378e8..25c8afe 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -221,7 +221,7 @@
* per-CPU workqueues:
*/
struct workqueue_struct {
- unsigned int flags; /* I: WQ_* flags */
+ unsigned int flags; /* W: WQ_* flags */
union {
struct cpu_workqueue_struct __percpu *pcpu;
struct cpu_workqueue_struct *single;
@@ -240,6 +240,7 @@
mayday_mask_t mayday_mask; /* cpus requesting rescue */
struct worker *rescuer; /* I: rescue worker */
+ int nr_drainers; /* W: drain in progress */
int saved_max_active; /* W: saved cwq max_active */
const char *name; /* I: workqueue name */
#ifdef CONFIG_LOCKDEP
@@ -990,7 +991,7 @@
debug_work_activate(work);
/* if dying, only works from the same workqueue are allowed */
- if (unlikely(wq->flags & WQ_DYING) &&
+ if (unlikely(wq->flags & WQ_DRAINING) &&
WARN_ON_ONCE(!is_chained_work(wq)))
return;
@@ -2381,6 +2382,54 @@
}
EXPORT_SYMBOL_GPL(flush_workqueue);
+/**
+ * drain_workqueue - drain a workqueue
+ * @wq: workqueue to drain
+ *
+ * Wait until the workqueue becomes empty. While draining is in progress,
+ * only chain queueing is allowed. IOW, only currently pending or running
+ * work items on @wq can queue further work items on it. @wq is flushed
+ * repeatedly until it becomes empty. The number of flushing is detemined
+ * by the depth of chaining and should be relatively short. Whine if it
+ * takes too long.
+ */
+void drain_workqueue(struct workqueue_struct *wq)
+{
+ unsigned int flush_cnt = 0;
+ unsigned int cpu;
+
+ /*
+ * __queue_work() needs to test whether there are drainers, is much
+ * hotter than drain_workqueue() and already looks at @wq->flags.
+ * Use WQ_DRAINING so that queue doesn't have to check nr_drainers.
+ */
+ spin_lock(&workqueue_lock);
+ if (!wq->nr_drainers++)
+ wq->flags |= WQ_DRAINING;
+ spin_unlock(&workqueue_lock);
+reflush:
+ flush_workqueue(wq);
+
+ for_each_cwq_cpu(cpu, wq) {
+ struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
+
+ if (!cwq->nr_active && list_empty(&cwq->delayed_works))
+ continue;
+
+ if (++flush_cnt == 10 ||
+ (flush_cnt % 100 == 0 && flush_cnt <= 1000))
+ pr_warning("workqueue %s: flush on destruction isn't complete after %u tries\n",
+ wq->name, flush_cnt);
+ goto reflush;
+ }
+
+ spin_lock(&workqueue_lock);
+ if (!--wq->nr_drainers)
+ wq->flags &= ~WQ_DRAINING;
+ spin_unlock(&workqueue_lock);
+}
+EXPORT_SYMBOL_GPL(drain_workqueue);
+
static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
bool wait_executing)
{
@@ -3011,34 +3060,10 @@
*/
void destroy_workqueue(struct workqueue_struct *wq)
{
- unsigned int flush_cnt = 0;
unsigned int cpu;
- /*
- * Mark @wq dying and drain all pending works. Once WQ_DYING is
- * set, only chain queueing is allowed. IOW, only currently
- * pending or running work items on @wq can queue further work
- * items on it. @wq is flushed repeatedly until it becomes empty.
- * The number of flushing is detemined by the depth of chaining and
- * should be relatively short. Whine if it takes too long.
- */
- wq->flags |= WQ_DYING;
-reflush:
- flush_workqueue(wq);
-
- for_each_cwq_cpu(cpu, wq) {
- struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
-
- if (!cwq->nr_active && list_empty(&cwq->delayed_works))
- continue;
-
- if (++flush_cnt == 10 ||
- (flush_cnt % 100 == 0 && flush_cnt <= 1000))
- printk(KERN_WARNING "workqueue %s: flush on "
- "destruction isn't complete after %u tries\n",
- wq->name, flush_cnt);
- goto reflush;
- }
+ /* drain it before proceeding with destruction */
+ drain_workqueue(wq);
/*
* wq list is used to freeze wq, remove from list after
