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.

Lai Jiangshan committed 14 years ago

Commit eab6d821 parent ea1abd61 file · +2 −16Browse files

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kernel/workqueue.c+2−16

@@ -1649,16 +1649,8 @@ static void busy_worker_rebind_fn(struct work_struct *work) · 1648 unmodified lines
1649	1649	struct worker *worker = container_of(work, struct worker, rebind_work);
1650	1650	struct global_cwq *gcwq = worker->pool->gcwq;
1651	1651
1652		− worker_maybe_bind_and_lock(worker);
1653		−
1654		− /*
1655		− * %WORKER_REBIND must be cleared even if the above binding failed;
1656		− * otherwise, we may confuse the next CPU_UP cycle or oops / get
1657		− * stuck by calling idle_worker_rebind() prematurely. If CPU went
1658		− * down again inbetween, %WORKER_UNBOUND would be set, so clearing
1659		− * %WORKER_REBIND is always safe.
1660		− */
1661		− worker_clr_flags(worker, WORKER_REBIND);
	1652	+ if (worker_maybe_bind_and_lock(worker))
	1653	+ worker_clr_flags(worker, WORKER_UNBOUND);
1662	1654
1663	1655	spin_unlock_irq(&gcwq->lock);
1664	1656	}
@@ -1721,15 +1713,9 @@ static void rebind_workers(struct global_cwq *gcwq) · 56 unmodified lines
1721	1713
1722	1714	/* rebind busy workers */
1723	1715	for_each_busy_worker(worker, i, pos, gcwq) {
1724		− unsigned long worker_flags = worker->flags;
1725	1716	struct work_struct *rebind_work = &worker->rebind_work;
1726	1717	struct workqueue_struct *wq;
1727	1718
1728		− /* morph UNBOUND to REBIND atomically */
1729		− worker_flags &= ~WORKER_UNBOUND;
1730		− worker_flags \|= WORKER_REBIND;
1731		− ACCESS_ONCE(worker->flags) = worker_flags;
1732		−
1733	1719	if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
1734	1720	work_data_bits(rebind_work)))
1735	1721	continue;