linux-kernel - Re: [PATCH] tools/memory-model: Remove lock-final checking in lock.cat

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Message-ID: <20200226235942.GR69864@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net>
Date:   Thu, 27 Feb 2020 07:59:42 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
        Andrea Parri <parri.andrea@...il.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Akira Yokosawa <akiyks@...il.com>,
        Daniel Lustig <dlustig@...dia.com>, linux-arch@...r.kernel.org
Subject: Re: [PATCH] tools/memory-model: Remove lock-final checking in
 lock.cat

On Wed, Feb 26, 2020 at 09:58:12AM -0500, Alan Stern wrote:
> On Wed, 26 Feb 2020, Boqun Feng wrote:
> 
> > In commit 30b795df11a1 ("tools/memory-model: Improve mixed-access
> > checking in lock.cat"), we have added the checking to disallow any
> > normal memory access to lock variables, and this checking is stronger
> > than lock-final. So remove the lock-final checking as it's unnecessary
> > now.
> 
> I don't understand this description.  Why do you say that the
> normal-access checking is stronger than the lock-final check?
> 
> > Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> > ---
> >  tools/memory-model/lock.cat | 3 ---
> >  1 file changed, 3 deletions(-)
> > 
> > diff --git a/tools/memory-model/lock.cat b/tools/memory-model/lock.cat
> > index 6b52f365d73a..827a3646607c 100644
> > --- a/tools/memory-model/lock.cat
> > +++ b/tools/memory-model/lock.cat
> > @@ -54,9 +54,6 @@ flag ~empty LKR \ domain(lk-rmw) as unpaired-LKR
> >   *)
> >  empty ([LKW] ; po-loc ; [LKR]) \ (po-loc ; [UL] ; po-loc) as lock-nest
> >  
> > -(* The final value of a spinlock should not be tested *)
> > -flag ~empty [FW] ; loc ; [ALL-LOCKS] as lock-final
> > -
> >  (*
> >   * Put lock operations in their appropriate classes, but leave UL out of W
> >   * until after the co relation has been generated.
> 
> With this check removed, what will prevent people from writing litmus 
> tests like this?
> 

You are right, one thing I was missing is although FW is a subset of M,
however FW & IW is not empty. Thanks! I will drop this.

Regards,
Boqun

> C test
> 
> {
> 	spinlock_t s;
> }
> 
> ...
> 
> exists (s=0)
> 
> Alan
>