linux-kernel - Re: [PATCH v3 07/15] lockdep: Implement crossrelease feature

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Date:   Wed, 14 Sep 2016 10:01:14 +0900
From:   Byungchul Park <max.byungchul.park@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Byungchul Park <byungchul.park@....com>,
        Ingo Molnar <mingo@...nel.org>, tglx@...utronix.de,
        Michel Lespinasse <walken@...gle.com>, boqun.feng@...il.com,
        kirill@...temov.name,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, npiggin@...il.com
Subject: Re: [PATCH v3 07/15] lockdep: Implement crossrelease feature

On Wed, Sep 14, 2016 at 6:42 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, Sep 13, 2016 at 09:38:29PM +0200, Peter Zijlstra wrote:
>
>> > > I _think_ you propose to keep track of all prior held locks and then use
>> > > the union of the held list on the block-chain with the prior held list
>> > > from the complete context.
>> >
>> > Almost right. Only thing we need to do to consider the union is to
>> > connect two chains of two contexts by adding one dependency 'b -> a'.
>>
>> Sure, but how do you arrive at which connection to make. The document is
>> entirely silent on this crucial point.
>>
>> The union between the held-locks of the blocked and prev-held-locks of
>> the release should give a fair indication I think, but then, I've not
>> thought too hard on this yet.
>
> s/union/intersection/
>
> those that are in both sets.

Precisely speaking, I introduces separate chains.

For example,

1. Held-locks of the blocked,
A -> B -> C (which original lockdep builds)

2. Prev-held-locks of the release
G -> H -> I (which original lockdep builds, too)

3. Cross chain (which I introduced newly)
C -> G

Then the 'A -> B -> C -> G -> H -> I' can be traversed
when bfs is performed.

-- 
Thanks,
Byungchul