linux-kernel - Re: [PATCH 2/3] LKMM: Add litmus test for RCU GP guarantee where reader stores

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Date:   Fri, 20 Mar 2020 16:56:59 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Joel Fernandes <joel@...lfernandes.org>
cc:     linux-kernel@...r.kernel.org, Akira Yokosawa <akiyks@...il.com>,
        Andrea Parri <parri.andrea@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        <linux-arch@...r.kernel.org>, Luc Maranget <luc.maranget@...ia.fr>,
        Nicholas Piggin <npiggin@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH 2/3] LKMM: Add litmus test for RCU GP guarantee where
 reader stores

On Fri, 20 Mar 2020, Joel Fernandes wrote:

> On Fri, Mar 20, 2020 at 11:03:30AM -0400, Alan Stern wrote:
> > On Fri, 20 Mar 2020, Joel Fernandes (Google) wrote:
> > 
> > > This adds an example for the important RCU grace period guarantee, which
> > > shows an RCU reader can never span a grace period.
> > > 
> > > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> > > ---
> > >  .../litmus-tests/RCU+sync+read.litmus         | 37 +++++++++++++++++++
> > >  1 file changed, 37 insertions(+)
> > >  create mode 100644 tools/memory-model/litmus-tests/RCU+sync+read.litmus
> > > 
> > > diff --git a/tools/memory-model/litmus-tests/RCU+sync+read.litmus b/tools/memory-model/litmus-tests/RCU+sync+read.litmus
> > > new file mode 100644
> > > index 0000000000000..73557772e2a32
> > > --- /dev/null
> > > +++ b/tools/memory-model/litmus-tests/RCU+sync+read.litmus
> > 
> > Do these new tests really belong here?  I thought we were adding a new 
> > directory under Documentation/ for litmus tests that illustrate parts 
> > of the LKMM or memory-barriers.txt.
> > 
> > By contrast, the tests under tools/memory-model are merely to show 
> > people what litmus tests look like and how they should be written.
> 
> I could add it to tools/memory-model/Documentation/ under a new
> 'examples' directory there. We could also create an 'rcu' directory in
> tools/memory-model/litmus-tests/ and add these there. Thoughts?

What happened was that about a month ago, Boqun Feng added
Documentation/atomic-tests for litmus tests related to handling of
atomic_t types (see
<https://marc.info/?l=linux-kernel&m=158276408609029&w=2>.)  Should we
interpose an extra directory level, making it
Documentation/litmus-tests/atomic?  Or
Documentation/LKMM-litmus-tests/atomic?

Then the new tests added here could go into
Documentation/litmus-tests/rcu, or whatever.

Alan