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Commit eab6d828 authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Tejun Heo
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workqueue: WORKER_REBIND is no longer necessary for busy rebinding 



Because the old unbind/rebinding implementation wasn't atomic w.r.t.
GCWQ_DISASSOCIATED manipulation which is protected by
global_cwq->lock, we had to use two flags, WORKER_UNBOUND and
WORKER_REBIND, to avoid incorrectly losing all NOT_RUNNING bits with
back-to-back CPU hotplug operations; otherwise, completion of
rebinding while another unbinding is in progress could clear UNBIND
prematurely.

Now that both unbind/rebinding are atomic w.r.t. GCWQ_DISASSOCIATED,
there's no need to use two flags.  Just one is enough.  Don't use
WORKER_REBIND for busy rebinding.

tj: Updated description.

Signed-off-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent ea1abd61

kernel/workqueue.c

+2 −16
Original line number Diff line number Diff line
@@ -1649,16 +1649,8 @@ static void busy_worker_rebind_fn(struct work_struct *work) 
	struct worker *worker = container_of(work, struct worker, rebind_work);

	struct global_cwq *gcwq = worker->pool->gcwq;



	worker_maybe_bind_and_lock(worker);



	/*

	 * %WORKER_REBIND must be cleared even if the above binding failed;

	 * otherwise, we may confuse the next CPU_UP cycle or oops / get

	 * stuck by calling idle_worker_rebind() prematurely.  If CPU went

	 * down again inbetween, %WORKER_UNBOUND would be set, so clearing

	 * %WORKER_REBIND is always safe.

	 */

	worker_clr_flags(worker, WORKER_REBIND);

	if (worker_maybe_bind_and_lock(worker))

		worker_clr_flags(worker, WORKER_UNBOUND);



	spin_unlock_irq(&gcwq->lock);

}
@@ -1721,15 +1713,9 @@ static void rebind_workers(struct global_cwq *gcwq) 


	/* rebind busy workers */

	for_each_busy_worker(worker, i, pos, gcwq) {

		unsigned long worker_flags = worker->flags;

		struct work_struct *rebind_work = &worker->rebind_work;

		struct workqueue_struct *wq;



		/* morph UNBOUND to REBIND atomically */

		worker_flags &= ~WORKER_UNBOUND;

		worker_flags |= WORKER_REBIND;

		ACCESS_ONCE(worker->flags) = worker_flags;



		if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,

				     work_data_bits(rebind_work)))

			continue;