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SubjectRe: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation
On Mon, Sep 04, 2017 at 01:42:48PM +0200, Peter Zijlstra wrote:
> On Mon, Sep 04, 2017 at 10:30:32AM +0900, Byungchul Park wrote:
> > On Fri, Sep 01, 2017 at 06:38:52PM +0200, Peter Zijlstra wrote:
> > > And get tangled up with the workqueue annotation again, no thanks.
> > > Having the first few works see the thread setup isn't worth it.
> > >
> > > And your work_id annotation had the same problem.
> >
> > I keep asking you for an example because I really understand you.
> >
> > Fix my problematic example with your patches,
> >
> > or,
> >
> > Show me a problematic scenario with my original code, you expect.
> >
> > Whatever, it would be helpful to understand you.
>
> I _really_ don't understand what you're worried about. Is it the kthread
> create and workqueue init or the pool->lock that is released/acquired in
> process_one_work()?

s/in process_one_work()/in all worker code including setup code/

Original code was already designed to handle real dependencies well. But
you invalidated it _w/o_ any reason, that's why I don't agree with your
patches. Your patches only do avoiding the wq issue now we focus on.

Look at:

worker thread another context
------------- ---------------
wait_for_completion()
|
| (1)
v
+---------+
| Work A | (2)
+---------+
|
| (3)
v
+---------+
| Work B | (4)
+---------+
|
| (5)
v
+---------+
| Work C | (6)
+---------+
|
v

We have to consider whole context of the worker to build dependencies
with a crosslock e.g. wait_for_commplete().

Only thing we have to care here is to make all works e.g. (2), (4) and
(6) independent, because workqueue does _concurrency control_. As I said
last year at the very beginning, for works not applied the control e.g.
max_active == 1, we don't need that isolation. I said, it's a future work.

It would have been much easier to communicate with each other if you
*tried* to understand my examples like now or you *tried* to give me one
example at least. You didn't even *try*. Only thing I want to ask you
for is to *try* to understand my opinions on conflicts.

Now, understand what I intended? Still unsufficient?

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