[PATCH 3/3] workqueue: remove get_online_cpus() from apply_workqueue_attrs()

[Lai Jiangshan]

There are two aims for get_online_cpus():
  1) Protects cpumask_of_node(node). (CPUs should stay stable)
  2) Protects the pwq-allocation and installation

But both aims are settled by other methods in previous patches:
cpumask_of_node(node) is replaced by wq_unbound_online_cpumask, and
the pwq-allocation and installation are changed to be protected by
wq_pool_mutex.  Now the get_online_cpus() is no reason to exist,
remove it!

Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
---
 kernel/workqueue.c |   15 ++-------------
 1 files changed, 2 insertions(+), 13 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 9bc3a87..63a8000 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3776,13 +3776,6 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
 	 */
 	copy_workqueue_attrs(tmp_attrs, new_attrs);
 
-	/*
-	 * CPUs should stay stable across pwq creations and installations.
-	 * Pin CPUs, determine the target cpumask for each node and create
-	 * pwqs accordingly.
-	 */
-	get_online_cpus();
-
 	mutex_lock(&wq_pool_mutex);
 
 	/*
@@ -3827,7 +3820,6 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
 
 	mutex_unlock(&wq_pool_mutex);
 
-	put_online_cpus();
 	ret = 0;
 	/* fall through */
 out_free:
@@ -3842,7 +3834,6 @@ enomem_pwq:
 		if (pwq_tbl && pwq_tbl[node] != dfl_pwq)
 			free_unbound_pwq(pwq_tbl[node]);
 	mutex_unlock(&wq_pool_mutex);
-	put_online_cpus();
 enomem:
 	ret = -ENOMEM;
 	goto out_free;
@@ -3921,10 +3912,8 @@ static void wq_update_unbound_numa(struct workqueue_struct *wq, int cpu)
 	}
 
 	/*
-	 * Install the new pwq.  As this function is called only from CPU
-	 * hotplug callbacks and applying a new attrs is wrapped with
-	 * get/put_online_cpus(), @wq->unbound_attrs couldn't have changed
-	 * inbetween.
+	 * Install the new pwq.  As this function is called with wq_pool_mutex
+	 * held, @wq->unbound_attrs couldn't have changed inbetween.
 	 */
 	mutex_lock(&wq->mutex);
 	old_pwq = numa_pwq_tbl_install(wq, node, pwq);
-- 
1.7.4.4

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