On Wed, Aug 30, 2017 at 11:09:53AM +0900, Byungchul Park wrote:
> On Tue, Aug 29, 2017 at 10:59:39AM +0200, Peter Zijlstra wrote:
> > Subject: lockdep: Untangle xhlock history save/restore from task
> > independence
> >
> > Where XHLOCK_{SOFT,HARD} are save/restore points in the xhlocks[] to
> > ensure the temporal IRQ events don't interact with task state, the
> > XHLOCK_PROC is a fundament different beast that just happens to share
> > the interface.
> >
> > The purpose of XHLOCK_PROC is to annotate independent execution inside
> > one task. For example workqueues, each work should appear to run in its
> > own 'pristine' 'task'.
> >
> > Remove XHLOCK_PROC in favour of its own interface to avoid confusion.
>
> Much better to me than the patch you did previously, but, see blow.
>
> > Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> > ---
> > diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> > index c0331891dec1..ab3c0dc8c7ed 100644
> > --- a/kernel/workqueue.c
> > +++ b/kernel/workqueue.c
> > @@ -2107,14 +2107,14 @@ __acquires(&pool->lock)
> > * Which would create W1->C->W1 dependencies, even though there is no
> > * actual deadlock possible. There are two solutions, using a
> > * read-recursive acquire on the work(queue) 'locks', but this will then
> > - * hit the lockdep limitation on recursive locks, or simly discard
> > + * hit the lockdep limitation on recursive locks, or simply discard
> > * these locks.
> > *
> > * AFAICT there is no possible deadlock scenario between the
> > * flush_work() and complete() primitives (except for single-threaded
> > * workqueues), so hiding them isn't a problem.
> > */
> > - crossrelease_hist_start(XHLOCK_PROC, true);
> > + lockdep_invariant_state(true);
>
> This is what I am always curious about. It would be ok if you agree with
> removing this work-around after fixing acquire things in wq. But, you
> keep to say this is essencial.
>
> You should focus on what dependencies actually are, than saparating
> contexts unnecessarily. Of course, we have to do it for each work, _BUT_
> not between outside of work and each work since there might be
> dependencies between them certainly.
You have never answered it. I'm curious about your answer. If you can't,
I think you have to revert all your patches. All yours are wrong.
