linux-kernel - Re: [PATCH 3/3] tools: memory-model: Improve data-race detection

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Message-ID: <Pine.LNX.4.44L0.1906231112300.24649-100000@netrider.rowland.org>
Date:   Sun, 23 Jun 2019 11:15:06 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Akira Yokosawa <akiyks@...il.com>
cc:     "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Nicholas Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] tools: memory-model: Improve data-race detection

On Sun, 23 Jun 2019, Akira Yokosawa wrote:

> Hi Paul and Alan,
> 
> On 2019/06/22 8:54, Paul E. McKenney wrote:
> > On Fri, Jun 21, 2019 at 10:25:23AM -0400, Alan Stern wrote:
> >> On Fri, 21 Jun 2019, Andrea Parri wrote:
> >>
> >>> On Thu, Jun 20, 2019 at 11:55:58AM -0400, Alan Stern wrote:
> >>>> Herbert Xu recently reported a problem concerning RCU and compiler
> >>>> barriers.  In the course of discussing the problem, he put forth a
> >>>> litmus test which illustrated a serious defect in the Linux Kernel
> >>>> Memory Model's data-race-detection code.
> 
> I was not involved in the mail thread and wondering what the litmus test
> looked like. Some searching of the archive has suggested that Alan presented
> a properly formatted test based on Herbert's idea in [1].
> 
> [1]: https://lore.kernel.org/lkml/Pine.LNX.4.44L0.1906041026570.1731-100000@iolanthe.rowland.org/

Yes, that's it.  The test is also available at:

https://github.com/paulmckrcu/litmus/blob/master/manual/plain/C-S-rcunoderef-2.litmus

Alan

> If this is the case, adding the link (or message id) in the change
> log would help people see the circumstances, I suppose.
> Paul, can you amend the change log?
> 
> I ran herd7 on said litmus test at both "lkmm" and "dev" of -rcu and
> confirmed that this patch fixes the result.
> 
> So,
> 
> Tested-by: Akira Yokosawa <akiyks@...il.com>
> 
>         Thanks, Akira