linux-kernel - Re: [PATCH RFC LKMM 7/7] tools/memory-model: Dynamically check SRCU lock-to-unlock matching

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Message-Id: <20190111214446.GL1215@linux.ibm.com>
Date:   Fri, 11 Jan 2019 13:44:46 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Andrea Parri <andrea.parri@...rulasolutions.com>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.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, willy@...radead.org
Subject: Re: [PATCH RFC LKMM 7/7] tools/memory-model: Dynamically check SRCU
 lock-to-unlock matching

On Fri, Jan 11, 2019 at 12:20:45AM +0100, Andrea Parri wrote:
> > > I'm not all that exited about spreading version requirements in the
> > > source: we report this requirement in our README, and apparently we
> > > already struggle to keep this information up-to-date.  So what about
> > > squashing something like the below (assume that 7.52 will be released
> > > by the time this patch hit mainline; if this won't be the case, we
> > > may consider using the development version 7.51+6)? notice that this
> > > also removes an (obsolete, at this point) comment from lock.cat.
> > 
> > Sounds like a very good point to me!
> > 
> > Should have pointers in the various files to the README file?  Or maybe
> > get people used to using scripting that checks versions?  Or maybe
> > after answering questions for some time, people will get used to
> > checking versions?
> 
> As discussed off-list: I have no strong opinion on this regard, well,
> except that I think we ought to fix the README, somehow (consider my
> diff below as a first proposal).  Akira actually preceded me on this
> and suggested another solution [1].
> 
>   Andrea
> 
> [1] http://lkml.kernel.org/r/04d15c18-d210-e3da-01e2-483eff135cb7@gmail.com

My concern with this approach is that it seems to me to implicitly promise
that herd will provide backwards compatibility, which is a real pain to
test, let alone to provide.  Yes, the latest version of herd probably
supports latest mainline, but will five-years-from-now herd work correctly
on the .bell, .cat, and .def files from current mainline?

							Thanx, Paul

> > >   Andrea
> > > 
> > > diff --git a/tools/memory-model/README b/tools/memory-model/README
> > > index 9d7d4f23503fd..b362a41358fa1 100644
> > > --- a/tools/memory-model/README
> > > +++ b/tools/memory-model/README
> > > @@ -20,8 +20,8 @@ that litmus test to be exercised within the Linux kernel.
> > >  REQUIREMENTS
> > >  ============
> > >  
> > > -Version 7.49 of the "herd7" and "klitmus7" tools must be downloaded
> > > -separately:
> > > +Version 7.52 or higher of the "herd7" and "klitmus7" tools must be
> > > +downloaded separately:
> > >  
> > >    https://github.com/herd/herdtools7
> > >  
> > > diff --git a/tools/memory-model/linux-kernel.cat b/tools/memory-model/linux-kernel.cat
> > > index 95bf45f1215fc..8dcb37835b613 100644
> > > --- a/tools/memory-model/linux-kernel.cat
> > > +++ b/tools/memory-model/linux-kernel.cat
> > > @@ -1,7 +1,5 @@
> > >  // SPDX-License-Identifier: GPL-2.0+
> > >  (*
> > > - * Requires herd version 7.51+6 or higher.
> > > - *
> > >   * Copyright (C) 2015 Jade Alglave <j.alglave@....ac.uk>,
> > >   * Copyright (C) 2016 Luc Maranget <luc.maranget@...ia.fr> for Inria
> > >   * Copyright (C) 2017 Alan Stern <stern@...land.harvard.edu>,
> > > diff --git a/tools/memory-model/lock.cat b/tools/memory-model/lock.cat
> > > index 305ded17e7411..a059d1a6d8a29 100644
> > > --- a/tools/memory-model/lock.cat
> > > +++ b/tools/memory-model/lock.cat
> > > @@ -6,9 +6,6 @@
> > >  
> > >  (*
> > >   * Generate coherence orders and handle lock operations
> > > - *
> > > - * Warning: spin_is_locked() crashes herd7 versions strictly before 7.48.
> > > - * spin_is_locked() is functional from herd7 version 7.49.
> > >   *)
> > >  
> > >  include "cross.cat"
> > > 
> > > 
> > > 
> > > > + *
> > > >   * Copyright (C) 2015 Jade Alglave <j.alglave@....ac.uk>,
> > > >   * Copyright (C) 2016 Luc Maranget <luc.maranget@...ia.fr> for Inria
> > > >   * Copyright (C) 2017 Alan Stern <stern@...land.harvard.edu>,
> > > > diff --git a/tools/memory-model/linux-kernel.def b/tools/memory-model/linux-kernel.def
> > > > index 1d6a120cde14..0c3f0ef486f4 100644
> > > > --- a/tools/memory-model/linux-kernel.def
> > > > +++ b/tools/memory-model/linux-kernel.def
> > > > @@ -49,7 +49,7 @@ synchronize_rcu_expedited() { __fence{sync-rcu}; }
> > > >  
> > > >  // SRCU
> > > >  srcu_read_lock(X)  __srcu{srcu-lock}(X)
> > > > -srcu_read_unlock(X,Y) { __srcu{srcu-unlock}(X); }
> > > > +srcu_read_unlock(X,Y) { __srcu{srcu-unlock}(X,Y); }
> > > >  synchronize_srcu(X)  { __srcu{sync-srcu}(X); }
> > > >  
> > > >  // Atomic
> > > > -- 
> > > > 2.17.1
> > > > 
> > > 
> > 
>