linux-kernel - [PATCH 2/2] workqueue: Keep activate-order equals to queue

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Date:	Tue, 18 Sep 2012 16:36:53 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Cc:	Lai Jiangshan <laijs@...fujitsu.com>
Subject: [PATCH 2/2] workqueue: Keep activate-order equals to queue_work()-order

The whole workqueue.c keeps activate-order equals to queue_work()-order
in any given cwq except workqueue_set_max_active().

If this order is not kept, something may be not good:

first_work_fn() { release some resource; }
second_work_fn() { wait and request the resource; use resource; }

1. user queues the first work.	# ->max_active is low, is queued on ->delayed_works.
2. someone increases the >max_active via workqueue_set_max_active()
3. user queues the second work.	# queued on cwq->pool.

When the second work is launched to execute, it waits the first work
to release the resource. But the first work is still in ->delayed_works,
it waits the first work to finish and them it can be activated.

It is bad. we fix it by activating the first work in the step 2.

I can't fully determine that it is workqueue's responsibility
or the user's responsibility.
If it is workqueue's responsibility, the patch needs go to -stable.
If it is user's responsibility. it is a nice cleanup, it can go to for-next.
I prefer it is workqueue's responsibility.

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
 kernel/workqueue.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index d0ca063..8783414 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3458,7 +3458,7 @@ void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)

 		if (!(wq->flags & WQ_FREEZABLE) ||
 		    !(gcwq->flags & GCWQ_FREEZING))
-			get_cwq(gcwq->cpu, wq)->max_active = max_active;
+			cwq_set_max_active(get_cwq(gcwq->cpu, wq), max_active);

 		spin_unlock_irq(&gcwq->lock);
 	}
-- 
1.7.4.4

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