linux-kernel - Re: Plain accesses and data races in the Linux Kernel Memory Model

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Message-ID: <Pine.LNX.4.44L0.1901151002040.1408-100000@iolanthe.rowland.org>
Date:   Tue, 15 Jan 2019 10:03:26 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Dmitry Vyukov <dvyukov@...gle.com>
cc:     "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        LKMM Maintainers -- Akira Yokosawa <akiyks@...il.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>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Plain accesses and data races in the Linux Kernel Memory Model

On Tue, 15 Jan 2019, Dmitry Vyukov wrote:

> On Tue, Jan 15, 2019 at 12:54 AM Paul E. McKenney <paulmck@...ux.ibm.com> wrote:
> >
> > On Mon, Jan 14, 2019 at 02:41:49PM -0500, Alan Stern wrote:
> > > The patch below is my first attempt at adapting the Linux Kernel
> > > Memory Model to handle plain accesses (i.e., those which aren't
> > > specially marked as READ_ONCE, WRITE_ONCE, acquire, release,
> > > read-modify-write, or lock accesses).  This work is based on an
> > > initial proposal created by Andrea Parri back in December 2017,
> > > although it has grown a lot since then.
> >
> > Hello, Alan,
> >
> > Good stuff!!!
> >
> > I tried applying this in order to test it against the various litmus
> > tests, but no joy.  Could you please tell me what commit is this patch
> > based on?
> >
> >                                                         Thanx, Paul
> >
> > > The adaptation involves two main aspects: recognizing the ordering
> > > induced by plain accesses and detecting data races.  They are handled
> > > separately.  In fact, the code for figuring out the ordering assumes
> > > there are no data races (the idea being that if a data race is
> > > present then pretty much anything could happen, so there's no point
> > > worrying about it -- obviously this will have to be changed if we want
> > > to cover seqlocks).
> 
> Hi Alan,
> 
> Is there a mailing list dedicated to this effort? Private messages
> tend to lost over time, no archive, not possible to send a link or
> show full history to anybody, etc.

No specific mailing list.  We've been relying on LKML.

> Re seqlocks, strictly saying defining races for seqlocks is not
> necessary. Seqlocks can be expressed without races in C by using
> relaxed atomic loads within the read critical section. We may consider
> this option as well.

That seems like a reasonable approach.

Alan