workqueue: reimplement is_chained_work() using current_wq_worker()

is_chained_work() was added before current_wq_worker() and implemented
its own ham-fisted way of finding out whether %current is a workqueue
worker - it iterates through all possible workers.

Drop the custom implementation and reimplement using
current_wq_worker().

Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 0d26ab3aee59c36e47e7bf10a455ebd49b91989f..ea7f696f1060783d7b074792f9701b46fb408ee3 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1159,35 +1159,18 @@ static void insert_work(struct cpu_workqueue_struct *cwq,
 
 /*
  * Test whether @work is being queued from another work executing on the
- * same workqueue.  This is rather expensive and should only be used from
- * cold paths.
+ * same workqueue.
  */
 static bool is_chained_work(struct workqueue_struct *wq)
 {
-       unsigned long flags;
-       unsigned int cpu;
-
-       for_each_cwq_cpu(cpu, wq) {
-               struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
-               struct worker_pool *pool = cwq->pool;
-               struct worker *worker;
-               struct hlist_node *pos;
-               int i;
+       struct worker *worker;
 
-               spin_lock_irqsave(&pool->lock, flags);
-               for_each_busy_worker(worker, i, pos, pool) {
-                       if (worker->task != current)
-                               continue;
-                       spin_unlock_irqrestore(&pool->lock, flags);
-                       /*
-                        * I'm @worker, no locking necessary.  See if @work
-                        * is headed to the same workqueue.
-                        */
-                       return worker->current_cwq->wq == wq;
-               }
-               spin_unlock_irqrestore(&pool->lock, flags);
-       }
-       return false;
+       worker = current_wq_worker();
+       /*
+        * Return %true iff I'm a worker execuing a work item on @wq.  If
+        * I'm @worker, it's safe to dereference it without locking.
+        */
+       return worker && worker->current_cwq->wq == wq;
 }
 
 static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,