linux-kernel - Re: [RESEND PATCH 1/3] completion: Add support for initializing completion with lockdep

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Date:   Fri, 20 Oct 2017 08:34:36 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Bart Van Assche <Bart.VanAssche@....com>
cc:     "mingo@...nel.org" <mingo@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "byungchul.park@....com" <byungchul.park@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "amir73il@...il.com" <amir73il@...il.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "oleg@...hat.com" <oleg@...hat.com>,
        "darrick.wong@...cle.com" <darrick.wong@...cle.com>,
        "johannes.berg@...el.com" <johannes.berg@...el.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "idryomov@...il.com" <idryomov@...il.com>,
        "tj@...nel.org" <tj@...nel.org>,
        "kernel-team@....com" <kernel-team@....com>,
        "david@...morbit.com" <david@...morbit.com>
Subject: Re: [RESEND PATCH 1/3] completion: Add support for initializing
 completion with lockdep_map

On Thu, 19 Oct 2017, Bart Van Assche wrote:
> On Wed, 2017-10-18 at 18:38 +0900, Byungchul Park wrote:
> > Sometimes, we want to initialize completions with sparate lockdep maps
> > to assign lock classes under control. For example, the workqueue code
> > manages lockdep maps, as it can classify lockdep maps properly.
> > Provided a function for that purpose.
> > 
> > Signed-off-by: Byungchul Park <byungchul.park@....com>
> > ---
> >  include/linux/completion.h | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/include/linux/completion.h b/include/linux/completion.h
> > index cae5400..182d56e 100644
> > --- a/include/linux/completion.h
> > +++ b/include/linux/completion.h
> > @@ -49,6 +49,13 @@ static inline void complete_release_commit(struct completion *x)
> >  	lock_commit_crosslock((struct lockdep_map *)&x->map);
> >  }
> >  
> > +#define init_completion_with_map(x, m)					\
> > +do {									\
> > +	lockdep_init_map_crosslock((struct lockdep_map *)&(x)->map,	\
> > +			(m)->name, (m)->key, 0);				\
> > +	__init_completion(x);						\
> > +} while (0)
> 
> Are there any completion objects for which the cross-release checking is
> useful?

All of them by definition.

> Are there any wait_for_completion() callers that hold a mutex or
> other locking object?

Yes, there are also cross completion dependencies. There have been such
bugs and I expect more to be unearthed.

I really have to ask what your motiviation is to fight the lockdep coverage
of synchronization objects tooth and nail?

Thanks,

	tglx