workqueue: Use the kmem_cache_free() instead of kfree() to release pwq

Currently, the kfree() be used for pwq objects allocated with
kmem_cache_alloc() in alloc_and_link_pwqs(), this isn't wrong.
but usually, use "trace_kmem_cache_alloc/trace_kmem_cache_free"
to track memory allocation and free. this commit therefore use
kmem_cache_free() instead of kfree() in alloc_and_link_pwqs()
and also consistent with release of the pwq in rcu_free_pwq().

Signed-off-by: Zqiang <qiang.zhang1211@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Author: Zqiang

kernel/workqueue.c

@@ -4610,8 +4610,12 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
 
 enomem:
 	if (wq->cpu_pwq) {
-		for_each_possible_cpu(cpu)
-			kfree(*per_cpu_ptr(wq->cpu_pwq, cpu));
+		for_each_possible_cpu(cpu) {
+			struct pool_workqueue *pwq = *per_cpu_ptr(wq->cpu_pwq, cpu);
+
+			if (pwq)
+				kmem_cache_free(pwq_cache, pwq);
+		}
 		free_percpu(wq->cpu_pwq);
 		wq->cpu_pwq = NULL;
 	}