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Subject[PATCH 2/2 wq/for-3.9] 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>
---
kernel/workqueue.c | 33 ++++++++-------------------------
1 file changed, 8 insertions(+), 25 deletions(-)

--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1159,35 +1159,18 @@ static void insert_work(struct cpu_workq

/*
* 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;
+ struct worker *worker;

- 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;
-
- 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,

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