linux-kernel - Re: [PATCH v4 15/15] lockdep: Crossrelease feature documentation

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Date:   Thu, 19 Jan 2017 10:54:28 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     'Boqun Feng' <boqun.feng@...il.com>, mingo@...nel.org,
        tglx@...utronix.de, walken@...gle.com, kirill@...temov.name,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        npiggin@...il.com
Subject: Re: [PATCH v4 15/15] lockdep: Crossrelease feature documentation

On Wed, Jan 18, 2017 at 03:12:55PM +0100, Peter Zijlstra wrote:
> On Wed, Jan 18, 2017 at 09:14:59PM +0900, byungchul.park wrote:
> 
> > +Example 3:
> > +
> > +   CONTEXT X		   CONTEXT Y
> > +   ---------		   ---------
> > +			   mutex_lock A
> > +   mutex_lock A
> > +   mutex_unlock A
> > +			   wait_for_complete B /* DEADLOCK */
> 
> Each line (across both columns) is a distinct point in time after the
> line before.
> 
> Therefore, this states that "mutex_unlock A" happens before
> "wait_for_completion B", which is clearly impossible.

I meant that all statements below mutex_lock A in X are already impossible.
So the order of those are meaningless. But.. I got what you mean.

> You don't have to remove everything after mutex_lock A, but the unlock
> must not happen before context Y does the unlock.

I will apply what you and boqun recommanded, from the next spin.

Thank you,
Byungchul