workqueue: separate out and refactor the locking of applying attrs

Applying attrs requires two locks: get_online_cpus() and wq_pool_mutex,
and this code is duplicated at two places (apply_workqueue_attrs() and
workqueue_set_unbound_cpumask()).  So we separate out this locking
code into apply_wqattrs_[un]lock() and do a minor refactor on
apply_workqueue_attrs().

The apply_wqattrs_[un]lock() will be also used on later patch for
ensuring attrs changes are properly synchronized.

tj: minor updates to comments

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -3621,24 +3621,21 @@ static void apply_wqattrs_commit(struct apply_wqattrs_ctx *ctx)
 	mutex_unlock(&ctx->wq->mutex);
 }
 
-/**
- * apply_workqueue_attrs - apply new workqueue_attrs to an unbound workqueue
- * @wq: the target workqueue
- * @attrs: the workqueue_attrs to apply, allocated with alloc_workqueue_attrs()
- *
- * Apply @attrs to an unbound workqueue @wq.  Unless disabled, on NUMA
- * machines, this function maps a separate pwq to each NUMA node with
- * possibles CPUs in @attrs->cpumask so that work items are affine to the
- * NUMA node it was issued on.  Older pwqs are released as in-flight work
- * items finish.  Note that a work item which repeatedly requeues itself
- * back-to-back will stay on its current pwq.
- *
- * Performs GFP_KERNEL allocations.
- *
- * Return: 0 on success and -errno on failure.
- */
-int apply_workqueue_attrs(struct workqueue_struct *wq,
-			  const struct workqueue_attrs *attrs)
+static void apply_wqattrs_lock(void)
+{
+	/* CPUs should stay stable across pwq creations and installations */
+	get_online_cpus();
+	mutex_lock(&wq_pool_mutex);
+}
+
+static void apply_wqattrs_unlock(void)
+{
+	mutex_unlock(&wq_pool_mutex);
+	put_online_cpus();
+}
+
+static int apply_workqueue_attrs_locked(struct workqueue_struct *wq,
+					const struct workqueue_attrs *attrs)
 {
 	struct apply_wqattrs_ctx *ctx;
 	int ret = -ENOMEM;
@@ -3651,14 +3648,6 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
 	if (WARN_ON((wq->flags & __WQ_ORDERED) && !list_empty(&wq->pwqs)))
 		return -EINVAL;
 
-	/*
-	 * 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);
-
 	ctx = apply_wqattrs_prepare(wq, attrs);
 
 	/* the ctx has been prepared successfully, let's commit it */
@@ -3667,14 +3656,39 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
 		ret = 0;
 	}
 
-	mutex_unlock(&wq_pool_mutex);
-	put_online_cpus();
-
 	apply_wqattrs_cleanup(ctx);
 
 	return ret;
 }
 
+/**
+ * apply_workqueue_attrs - apply new workqueue_attrs to an unbound workqueue
+ * @wq: the target workqueue
+ * @attrs: the workqueue_attrs to apply, allocated with alloc_workqueue_attrs()
+ *
+ * Apply @attrs to an unbound workqueue @wq.  Unless disabled, on NUMA
+ * machines, this function maps a separate pwq to each NUMA node with
+ * possibles CPUs in @attrs->cpumask so that work items are affine to the
+ * NUMA node it was issued on.  Older pwqs are released as in-flight work
+ * items finish.  Note that a work item which repeatedly requeues itself
+ * back-to-back will stay on its current pwq.
+ *
+ * Performs GFP_KERNEL allocations.
+ *
+ * Return: 0 on success and -errno on failure.
+ */
+int apply_workqueue_attrs(struct workqueue_struct *wq,
+			  const struct workqueue_attrs *attrs)
+{
+	int ret;
+
+	apply_wqattrs_lock();
+	ret = apply_workqueue_attrs_locked(wq, attrs);
+	apply_wqattrs_unlock();
+
+	return ret;
+}
+
 /**
  * wq_update_unbound_numa - update NUMA affinity of a wq for CPU hot[un]plug
  * @wq: the target workqueue
@@ -4799,10 +4813,9 @@ int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
 	if (!zalloc_cpumask_var(&saved_cpumask, GFP_KERNEL))
 		return -ENOMEM;
 
-	get_online_cpus();
 	cpumask_and(cpumask, cpumask, cpu_possible_mask);
 	if (!cpumask_empty(cpumask)) {
-		mutex_lock(&wq_pool_mutex);
+		apply_wqattrs_lock();
 
 		/* save the old wq_unbound_cpumask. */
 		cpumask_copy(saved_cpumask, wq_unbound_cpumask);
@@ -4815,9 +4828,8 @@ int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
 		if (ret < 0)
 			cpumask_copy(wq_unbound_cpumask, saved_cpumask);
 
-		mutex_unlock(&wq_pool_mutex);
+		apply_wqattrs_unlock();
 	}
-	put_online_cpus();
 
 	free_cpumask_var(saved_cpumask);
 	return ret;