linux-kernel - Re: [GIT PULL tools] Linux kernel memory model

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Message-ID: <20180209124112.GA21524@andrea>
Date:   Fri, 9 Feb 2018 13:41:12 +0100
From:   Andrea Parri <parri.andrea@...il.com>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Patrick Bellasi <patrick.bellasi@....com>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        stern@...land.harvard.edu, j.alglave@....ac.uk,
        luc.maranget@...ia.fr, boqun.feng@...il.com, will.deacon@....com,
        npiggin@...il.com, dhowells@...hat.com, elena.reshetova@...el.com,
        mhocko@...e.com, akiyks@...il.com
Subject: Re: [GIT PULL tools] Linux kernel memory model

On Fri, Feb 09, 2018 at 03:29:37AM -0800, Paul E. McKenney wrote:
> On Fri, Feb 09, 2018 at 10:11:10AM +0100, Andrea Parri wrote:
> > On Thu, Feb 08, 2018 at 09:02:19PM +0100, Peter Zijlstra wrote:
> > > On Thu, Feb 08, 2018 at 06:41:06PM +0000, Patrick Bellasi wrote:
> > > > Hi Paul,
> > > > thanks to you and all the involved guys for this useful tool.
> > > > 
> > > > I give it a try today and found that by installing herd7 by just
> > > > following the instruction in herdtools7/INSTALL.md, and precisely
> > > > installing it via:
> > > > 
> > > >    opam install herdtools7
> > > > 
> > > > it seems to give you a tool which fails to run the basic example in
> > > > your README with this error:
> > > > 
> > > >    File "./linux-kernel.def", line 44, characters 29-30: unexpected '-' (in macros)
> > > > 
> > > > As suggested by Will, by building instead herd7 HEAD (commit 44d69c2)
> > > > everything works fine.
> > > > 
> > > > Maybe it's a know issue, in case just ignore me. :)
> > > > 
> > > > Otherwise, maybe it can be worth to add to the README a note on which
> > > > minimum version of the herd7 tool is required.
> > > > 
> > > >  opma   version (not working)    : 7.47, Rev: exported
> > > >  master version (working for me) : 7.47+7(dev), Rev: 44d69c2b1b5ca0f97bd138899d31532ee5e4e084
> > > 
> > > Urgh. So that's why it wouldn't work.
> > > 
> > > I remember Paul saying you needed the latest version, which is why I
> > > rebuild from opam, but building top of git is a bit much.
> > 
> > +1
> > 
> > _Sadly_ enough, co-developers and I were aware of this issue,
> > but it was only mildly reported here (c.f.,
> > 
> >   https://marc.info/?l=linux-kernel&m=151638196427685&w=2 ).
> > 
> > This bisects to that (crazy):
> > 
> >   2d5fba7782d669c6a1cc577dbc3bf507780273bb
> >   ("linux-kernel*: Make RCU identifiers match ASPLOS paper")
> > 
> >   From repo.: https://github.com/aparri/memory-model
> > 
> > which not only did break 7.47, but also made the bell uglier
> > by mixing dashes and underscores in a very same block.
> > 
> > As a solution to this issue, I can envisage a partial revert
> > of that commit (just replace those dashes); Paul, Jade, Luc:
> > any better solution?
> > 
> > (Sorry for being late on IRC, glad this came out here,)
> 
> Or maybe a 7.48 release?

This would work, _prior upgrade. (This's not my call of course).

I do however want to iterate, looking again at the above commit:

 		'rb_dep (*smp_read_barrier_depends*) ||
-		'rcu_read_lock (*rcu_read_lock*)  ||
-		'rcu_read_unlock (*rcu_read_unlock*) ||
-		'sync (*synchronize_rcu*) ||
+		'rcu-lock (*rcu_read_lock*)  ||
+		'rcu-unlock (*rcu_read_unlock*) ||
+		'sync-rcu (*synchronize_rcu*) ||
 		'before_atomic (*smp_mb__before_atomic*) ||
 		'after_atomic (*smp_mb__after_atomic*) ||
 		'after_spinlock (*smp_mb__after_spinlock*)

The question arises: dash or underscore? This needs to be fixed.

  Andrea


> 
> 							Thanx, Paul
>