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Subject[PATCH wq/for-3.9] workqueue: make work_busy() test WORK_STRUCT_PENDING first
From: Lai Jiangshan <laijs@cn.fujitsu.com>

Currently, work_busy() first tests whether the work has a pool
associated with it and if not, considers it idle. This works fine
even for delayed_work.work queued on timer, as __queue_delayed_work()
sets cwq on delayed_work.work - a queued delayed_work always has its
cwq and thus pool associated with it.

However, we're about to update delayed_work queueing and this won't
hold. Update work_busy() such that it tests WORK_STRUCT_PENDING
before the associated pool. This doesn't make any noticeable behavior
difference now.

With work_pending() test moved, the function read a lot better with
"if (!pool)" test flipped to positive. Flip it.

While at it, lose the comment about now non-existent reentrant
workqueues.

tj: Reorganized the function and rewrote the description.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
Hey, Lai.

Did I get the reason right? Can you *please* try to explain "why" a
patch is needed / beneficial for future postings like I did above? I
get that writing in English could be a bit stressful (it's not my
mother tongue either and I struggled with it a lot and still do to
certain extent) but the language doesn't have to be perfect. You just
need to communicate main points of your rationale somehow.

Thanks.

kernel/workqueue.c | 16 ++++++----------
1 file changed, 6 insertions(+), 10 deletions(-)

--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3443,8 +3443,6 @@ EXPORT_SYMBOL_GPL(workqueue_congested);
* Test whether @work is currently pending or running. There is no
* synchronization around this function and the test result is
* unreliable and only useful as advisory hints or for debugging.
- * Especially for reentrant wqs, the pending state might hide the
- * running state.
*
* RETURNS:
* OR'd bitmask of WORK_BUSY_* bits.
@@ -3455,17 +3453,15 @@ unsigned int work_busy(struct work_struc
unsigned long flags;
unsigned int ret = 0;

- if (!pool)
- return 0;
-
- spin_lock_irqsave(&pool->lock, flags);
-
if (work_pending(work))
ret |= WORK_BUSY_PENDING;
- if (find_worker_executing_work(pool, work))
- ret |= WORK_BUSY_RUNNING;

- spin_unlock_irqrestore(&pool->lock, flags);
+ if (pool) {
+ spin_lock_irqsave(&pool->lock, flags);
+ if (find_worker_executing_work(pool, work))
+ ret |= WORK_BUSY_RUNNING;
+ spin_unlock_irqrestore(&pool->lock, flags);
+ }

return ret;
}

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