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.
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| @@ -1649,16 +1649,8 @@ static void busy_worker_rebind_fn(struct work_struct *work) · 1648 unmodified lines | |||
| 1649 | struct worker *worker = container_of(work, struct worker, rebind_work); | 1649 | struct worker *worker = container_of(work, struct worker, rebind_work); |
| 1650 | struct global_cwq *gcwq = worker->pool->gcwq; | 1650 | struct global_cwq *gcwq = worker->pool->gcwq; |
| 1651 | 1651 | ||
| 1652 | worker_maybe_bind_and_lock(worker); | 1652 | if (worker_maybe_bind_and_lock(worker)) |
| 1653 | 1653 | worker_clr_flags(worker, WORKER_UNBOUND); | |
| 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); | ||
| 1662 | 1654 | ||
| 1663 | spin_unlock_irq(&gcwq->lock); | 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 | /* rebind busy workers */ | 1714 | /* rebind busy workers */ |
| 1723 | for_each_busy_worker(worker, i, pos, gcwq) { | 1715 | for_each_busy_worker(worker, i, pos, gcwq) { |
| 1724 | unsigned long worker_flags = worker->flags; | ||
| 1725 | struct work_struct *rebind_work = &worker->rebind_work; | 1716 | struct work_struct *rebind_work = &worker->rebind_work; |
| 1726 | struct workqueue_struct *wq; | 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 | if (test_and_set_bit(WORK_STRUCT_PENDING_BIT, | 1719 | if (test_and_set_bit(WORK_STRUCT_PENDING_BIT, |
| 1734 | work_data_bits(rebind_work))) | 1720 | work_data_bits(rebind_work))) |
| 1735 | continue; | 1721 | continue; |