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    SubjectRE: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation
    > -----Original Message-----
    > From: Byungchul Park [mailto:byungchul.park@lge.com]
    > Sent: Friday, September 01, 2017 7:16 PM
    > To: Peter Zijlstra
    > Cc: mingo@kernel.org; tj@kernel.org; boqun.feng@gmail.com;
    > david@fromorbit.com; johannes@sipsolutions.net; oleg@redhat.com; linux-
    > kernel@vger.kernel.org; kernel-team@lge.com
    > Subject: Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation
    >
    > On Fri, Sep 01, 2017 at 11:47:47AM +0200, Peter Zijlstra wrote:
    > > On Fri, Sep 01, 2017 at 11:05:12AM +0900, Byungchul Park wrote:
    > > > On Thu, Aug 31, 2017 at 10:34:53AM +0200, Peter Zijlstra wrote:
    > > > > On Thu, Aug 31, 2017 at 05:15:01PM +0900, Byungchul Park wrote:
    > > > > > It's not important. Ok, check the following, instead:
    > > > > >
    > > > > > context X context Y
    > > > > > --------- ---------
    > > > > > wait_for_completion(C)
    > > > > > acquire(A)
    > > > > > release(A)
    > > > > > process_one_work()
    > > > > > acquire(B)
    > > > > > release(B)
    > > > > > work->fn()
    > > > > > complete(C)
    > > > > >
    > > > > > We don't need to lose C->A and C->B dependencies unnecessarily.
    > > > >
    > > > > I really can't be arsed about them. Its really only the first few
    > works
    > > > > that will retain that dependency anyway, even if you were to retain
    > > > > them.
    > > >
    > > > Wrong.
    > > >
    > > > Every 'work' doing complete() for different classes of completion
    > > > variable suffers from losing valuable dependencies, every time, not
    > > > first few ones.
    > >
    > > The moment you overrun the history array its gone. So yes, only the
    >
    > It would be gone _only_ at the time the history overrun, and then it
    > will be built again. So, you are wrong.
    >
    > Let me show you an example: (I hope you also show examples.)
    >
    > context X context Y
    > --------- ---------
    > wait_for_completion(D)
    > while (true)
    > acquire(A)
    > release(A)
    > process_one_work()
    > acquire(B)
    > release(B)
    > work->fn()
    > complete(C)
    > acquire(D)
    > release(D)
    >
    > When happening an overrun in a 'work', 'A' and 'B' will be gone _only_
    > at the time, and then 'D', 'A' and 'B' will be queued into the xhlock
    > *again* from the next loop on, and they can be used to generate useful
    > dependencies again.
    >
    > You are being confused now. Acquisitions we are focusing now are not
    > _stacked_ like hlocks, but _accumulated_ continuously onto the ring
    > buffer e.i. xhlock array.

    Agree?
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