linux-kernel - Re: [PATCH v2] tools/memory-model: Make compat with herd7 7.47 ("-" -> "

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Message-ID: <20180211115148.iylaqk3f53f2vgf4@gmail.com>
Date:   Sun, 11 Feb 2018 12:51:48 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Akira Yokosawa <akiyks@...il.com>, linux-kernel@...r.kernel.org,
        stern@...land.harvard.edu, parri.andrea@...il.com,
        will.deacon@....com, peterz@...radead.org, boqun.feng@...il.com,
        npiggin@...il.com, dhowells@...hat.com, j.alglave@....ac.uk,
        luc.maranget@...ia.fr, Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH v2] tools/memory-model: Make compat with herd7 7.47 ("-"
 -> "_")


* Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:

> On Sat, Feb 10, 2018 at 08:46:25AM +0900, Akira Yokosawa wrote:
> > >From 7c1f497a9a51e8db1a94c8a7ef0b74b235aaab88 Mon Sep 17 00:00:00 2001
> > From: Akira Yokosawa <akiyks@...il.com>
> > Date: Fri, 9 Feb 2018 04:51:05 -0800
> > Subject: [PATCH v2] tools/memory-model: Make compat with herd7 7.47 ("-" -> "_")
> > 
> > As of herd7 7.47, these '-'s are not permitted and end up in
> > errors such as:
> > 
> >     File "./linux-kernel.def", line 44, characters 29-30:
> >     unexpected '-' (in macros)
> > 
> > Partial revert of commit 2d5fba7782d6 ("linux-kernel*: Make RCU
> > identifiers match ASPLOS paper") in the repository at
> > https://github.com/aparri/memory-model can restore the compatibility
> > with herd7 7.47.
> > 
> > Reported-by: Patrick Bellasi <patrick.bellasi@....com>
> > Suggested-by: Andrea Parri <parri.andrea@...il.com>
> > Signed-off-by: Akira Yokosawa <akiyks@...il.com>
> > ---
> > Paul,
> > 
> > FWIW, this is a squashed version relative to patch 07/10 in the RFC series.
> 
> Thank you, Akira!
> 
> I am going to hold off on this for a bit to see if we can instead get
> a new release of herd7, but if we can't. this might well be a very good
> way to go.

I'm wondering:

> >  // RCU
> > -rcu_read_lock() { __fence{rcu-lock}; }
> > -rcu_read_unlock() { __fence{rcu-unlock};}
> > -synchronize_rcu() { __fence{sync-rcu}; }
> > -synchronize_rcu_expedited() { __fence{sync-rcu}; }
> > +rcu_read_lock() { __fence{rcu_lock}; }
> > +rcu_read_unlock() { __fence{rcu_unlock};}
> > +synchronize_rcu() { __fence{sync_rcu}; }
> > +synchronize_rcu_expedited() { __fence{sync_rcu}; }

What's the point of using '-' instead of '_'? In a program language syntax 
environment it's easy to confuse it with a '-' operator, and it also looks 
slightly sloppy and inconsistent if we sometimes have '_' and sometimes '-'.

If it used on purpose, to separate namespaces from kernel internal API names,
then that's rather obscure IMHO and then I'd rather suggest proper prefixes 
instead.

Thanks,

	Ingo