[PATCH 2/3 V2] workqueue: ensure the wq_worker_sleeping() see the right flags

[Lai Jiangshan]

The compiler may compile this code into TWO write/modify instructions.
		worker->flags &= ~WORKER_UNBOUND;
		worker->flags |= WORKER_REBIND;

so the other CPU may see the temporary of worker->flags which has
not WORKER_UNBOUND nor WORKER_REBIND, it will wrongly do local wake up.

So we simply change the code that WORKER_UNBOUND is cleared in
busy_worker_rebind_fn(), not in rebind_workers(). And REBIND is not
used for busy_worker, busy_worker_rebind_fn() knows itself need
to do rebind when it is called.

Because the rebind_workers() will wait busy_worker_rebind_fn() to
finish rebinding and clearing, the CPU can't be offline,
busy_worker_rebind_fn() will not clear the wrong WORKER_UNBOUND.

Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
---
 kernel/workqueue.c |    6 +-----
 1 files changed, 1 insertions(+), 5 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 5f63883..3e0bd20 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1354,7 +1354,7 @@ static void busy_worker_rebind_fn(struct work_struct *work)
 
 	/* CPU must be online at this point */
 	WARN_ON(!worker_maybe_bind_and_lock(worker));
-	worker_clr_flags(worker, WORKER_REBIND);
+	worker_clr_flags(worker, WORKER_UNBOUND);
 	spin_unlock_irq(&gcwq->lock);
 
 	/* all_cnt is only accessed by the bound CPU, don't need any lock */
@@ -1420,10 +1420,6 @@ static void rebind_workers(struct global_cwq *gcwq)
 	for_each_busy_worker(worker, i, pos, gcwq) {
 		struct work_struct *rebind_work = &worker->rebind_work;
 
-		/* morph UNBOUND to REBIND */
-		worker->flags &= ~WORKER_UNBOUND;
-		worker->flags |= WORKER_REBIND;
-
 		if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
 				     work_data_bits(rebind_work)))
 			continue;
-- 
1.7.4.4

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