[PATCH 3/7] workqueue: explicit way to wait for idles workers to finish

[Lai Jiangshan <laijs@cn.fujitsu.com>]

busy_worker_rebind_fn() can't return until all idle workers are rebound.
This order is ensured by rebind_workers() currently.

We use mutex_lock(&worker->pool->manager_mutex) to wait for all idle workers
to be rebound. this is an explicit way and it will ease the pain of
the rebind_workers().

The sleeping mutex_lock(&worker->pool->manager_mutex) must be put in the top of
busy_worker_rebind_fn(), because this busy worker thread can sleep
before the WORKER_REBIND is cleared, but can't sleep after
the WORKER_REBIND cleared.

It adds a small overhead to the unlikely path.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
 kernel/workqueue.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 90ada8f..f6e4394 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1337,6 +1337,13 @@ static void busy_worker_rebind_fn(struct work_struct *work)
 	struct worker *worker = container_of(work, struct worker, rebind_work);
 	struct global_cwq *gcwq = worker->pool->gcwq;
 
+	/*
+	 * Waiting all idle workers are rebound by competing on
+	 * pool->manager_mutex and waiting for rebind_workers() to finish up.
+	 */
+	mutex_lock(&worker->pool->manager_mutex);
+	mutex_unlock(&worker->pool->manager_mutex);
+
 	if (worker_maybe_bind_and_lock(worker))
 		worker_clr_flags(worker, WORKER_REBIND);
 
-- 
1.7.4.4