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From:   Xiongwei Song <sxwjean@gmail.com>
Date:   Mon, 24 May 2021 21:17:52 +0800
Message-ID: <CAEVVKH-Tun1Bh2BoYq_3UXXWgZMOHbmDu1jCMowWBj4uJ1MZuw@mail.gmail.com>
Subject: Re: [PATCH] docs: lockdep-design: correct the notation for writer
To:     Boqun Feng <boqun.feng@gmail.com>
Cc:     Waiman Long <llong@redhat.com>, Xiongwei Song <sxwjean@me.com>,
        peterz@infradead.org, mingo@redhat.com, will@kernel.org,
        corbet@lwn.net,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-doc@vger.kernel.org
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On Mon, May 24, 2021 at 6:33 PM Boqun Feng <boqun.feng@gmail.com> wrote:
>
> On Mon, May 24, 2021 at 12:24:00PM +0800, Xiongwei Song wrote:
> > On Fri, May 21, 2021 at 11:17 PM Waiman Long <llong@redhat.com> wrote:
> > >
> > > On 5/21/21 2:29 AM, Xiongwei Song wrote:
> > > > From: Xiongwei Song <sxwjean@gmail.com>
> > > >
> > > > The block condition matrix is using 'E' as the writer noation here, so it
> > > > would be better to use 'E' as the reminder rather than 'W'.
> > > >
> > > > Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
> > > > ---
> > > >   Documentation/locking/lockdep-design.rst | 2 +-
> > > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/Documentation/locking/lockdep-design.rst b/Documentation/locking/lockdep-design.rst
> > > > index 9f3cfca..c3b923a 100644
> > > > --- a/Documentation/locking/lockdep-design.rst
> > > > +++ b/Documentation/locking/lockdep-design.rst
> > > > @@ -462,7 +462,7 @@ Block condition matrix, Y means the row blocks the column, and N means otherwise
> > > >       | R | Y | Y | N |
> > > >       +---+---+---+---+
> > > >
> > > > -     (W: writers, r: non-recursive readers, R: recursive readers)
> > > > +     (E: writers, r: non-recursive readers, R: recursive readers)
> > > >
> > > >
> > > >   acquired recursively. Unlike non-recursive read locks, recursive read locks
> > >
> > > I would say it should be the other way around. Both W and E refer to the
> > > same type of lockers. W emphasizes writer aspect of it and E for
> > > exclusive. I think we should change the block condition matrix to use W
> > > instead of E.
> >
> > The doc uses 'E'  to describe dependency egdes too. Should we change them
> > to 'W'? Personally,  both 'W' and 'E' are fine.
> >
>
> I also think Waiman's suggestion is solid, there are two ways to
> classify locks:
>
> 1.      W (Writers), R (Recursive Readers), r (Non-recursive Readers)
>
> 2.      E (Exclusive locks), S (Shared locks), R (Recursive Readers),
>         N (Non-recursive locks)
>
> And the relations between them are as follow:
>
>         E = W
>         R = R
>         N = W \/ r
>         S = R \/ r
>
> , where "\/" is the set union.
>
> The story is that I used the way #1 at first, and later on realized way
> #2 is better for BFS implementation, also for reasoning, so here came
> this leftover..

Thanks for the explanation.

>
> If you are interested, go ahead sending a patch fixing this, otherwise,
> I will fix this.

Ok.  Let me fix.

Thanks,
Xiongwei
>
> Regards,
> Boqun
>
> > Thanks,
> > Xiongwei
> > >
> > > Cheers,
> > > Longman
> > >