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>

1 files changed, 8 insertions, 25 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 0d26ab3aee59..ea7f696f1060 100644
--- 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,