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Date: Wed, 18 Jan 2017 12:03:17 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Byungchul Park <byungchul.park@lge.com>
Cc: Boqun Feng <boqun.feng@gmail.com>, mingo@kernel.org,
        tglx@linutronix.de, walken@google.com, kirill@shutemov.name,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, npiggin@gmail.com
Subject: Re: [PATCH v4 15/15] lockdep: Crossrelease feature documentation
Message-ID: <20170118110317.GC6515@twins.programming.kicks-ass.net>
References: <1481260331-360-1-git-send-email-byungchul.park@lge.com>
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On Wed, Jan 18, 2017 at 07:53:47PM +0900, Byungchul Park wrote:
> On Wed, Jan 18, 2017 at 02:42:30PM +0800, Boqun Feng wrote:
> > On Fri, Dec 09, 2016 at 02:12:11PM +0900, Byungchul Park wrote:
> > [...]
> > > +Example 1:
> > > +
> > > +   CONTEXT X		   CONTEXT Y
> > > +   ---------		   ---------
> > > +   mutext_lock A
> > > +			   lock_page B
> > > +   lock_page B
> > > +			   mutext_lock A /* DEADLOCK */
> > 
> > s/mutext_lock/mutex_lock
> 
> Thank you.
> 
> > > +Example 3:
> > > +
> > > +   CONTEXT X		   CONTEXT Y
> > > +   ---------		   ---------
> > > +			   mutex_lock A
> > > +   mutex_lock A
> > > +   mutex_unlock A
> > > +			   wait_for_complete B /* DEADLOCK */
> > 
> > I think this part better be:
> > 
> >    CONTEXT X		   CONTEXT Y
> >    ---------		   ---------
> >    			   mutex_lock A
> >    mutex_lock A
> >    			   wait_for_complete B /* DEADLOCK */
> >    mutex_unlock A
> > 
> > , right? Because Y triggers DEADLOCK before X could run mutex_unlock().
> 
> There's no different between two examples.

There is..

> No matter which one is chosen, mutex_lock A in CONTEXT X cannot be passed.

But your version shows it does mutex_unlock() before CONTEXT Y does
wait_for_completion().

The thing about these diagrams is that both columns are assumed to have
the same timeline.