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: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
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@ -1649,16 +1649,8 @@ static void busy_worker_rebind_fn(struct work_struct *work)
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struct worker *worker = container_of(work, struct worker, rebind_work);
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struct global_cwq *gcwq = worker->pool->gcwq;
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worker_maybe_bind_and_lock(worker);
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/*
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* %WORKER_REBIND must be cleared even if the above binding failed;
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* otherwise, we may confuse the next CPU_UP cycle or oops / get
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* stuck by calling idle_worker_rebind() prematurely. If CPU went
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* down again inbetween, %WORKER_UNBOUND would be set, so clearing
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* %WORKER_REBIND is always safe.
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*/
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worker_clr_flags(worker, WORKER_REBIND);
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if (worker_maybe_bind_and_lock(worker))
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worker_clr_flags(worker, WORKER_UNBOUND);
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spin_unlock_irq(&gcwq->lock);
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}
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@ -1721,15 +1713,9 @@ static void rebind_workers(struct global_cwq *gcwq)
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/* rebind busy workers */
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for_each_busy_worker(worker, i, pos, gcwq) {
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unsigned long worker_flags = worker->flags;
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struct work_struct *rebind_work = &worker->rebind_work;
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struct workqueue_struct *wq;
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/* morph UNBOUND to REBIND atomically */
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worker_flags &= ~WORKER_UNBOUND;
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worker_flags |= WORKER_REBIND;
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ACCESS_ONCE(worker->flags) = worker_flags;
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if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
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work_data_bits(rebind_work)))
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continue;
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