linux-kernel - Re: [PATCH] tools/memory-model: Document herd7 (internal) representation

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Message-ID: <37bbf3c3-8951-41f8-b900-e81a885b949e@rowland.harvard.edu>
Date: Fri, 24 May 2024 16:04:09 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Andrea Parri <parri.andrea@...il.com>
Cc: will@...nel.org, peterz@...radead.org, boqun.feng@...il.com,
  npiggin@...il.com, dhowells@...hat.com, j.alglave@....ac.uk,
  luc.maranget@...ia.fr, paulmck@...nel.org, akiyks@...il.com,
  dlustig@...dia.com, joel@...lfernandes.org, linux-kernel@...r.kernel.org,
  linux-arch@...r.kernel.org, hernan.poncedeleon@...weicloud.com,
  jonas.oberhauser@...weicloud.com
Subject: Re: [PATCH] tools/memory-model: Document herd7 (internal)
 representation

On Fri, May 24, 2024 at 05:37:06PM +0200, Andrea Parri wrote:
> > - While checking the information below using herd7, I've observed some
> >   "strange" behavior with spin_is_locked() (perhaps, unsurprisingly...);
> >   IAC, that's also excluded from this table/submission.
> 
> For completeness, the behavior in question:
> 
> $ cat T.litmus 
> C T
> 
> {}
> 
> P0(spinlock_t *x)
> {
> 	int r0;
> 
> 	spin_lock(x);
> 	spin_unlock(x);
> 	r0 = spin_is_locked(x);
> }
> 
> $ herd7 -conf linux-kernel.cfg T.litmus
> Test T Required
> States 0
> Ok
> Witnesses
> Positive: 0 Negative: 0
> Condition forall (true)
> Observation T Never 0 0
> Time T 0.00
> Hash=6fa204e139ddddf2cb6fa963bad117c0
> 
> Haven't been using spin_is_locked for a while...  perhaps I'm doing
> something wrong?  (IAC, will have a closer look next week...)

I get the same empty result.  There's definitely something going wrong 
in the "with ... from cross(...)" lines in lock.cat.  I need to do some 
checking and testing.

Also, lock.cat doesn't check for R events that don't actually read from 
anything (which will happen when the spin_is_locked() call above 
generates an RL event).  This is a separate bug, easily fixed.

Alan