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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: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Lai Jiangshan 2012-09-18 09:59:22 -07:00 committed by Tejun Heo
parent ea1abd6197
commit eab6d82843
1 changed files with 2 additions and 16 deletions
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18
kernel/workqueue.c
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@ -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;