linux-kernel - Re: Internal vs. external barriers (was: Re: Interesting LKMM litmus test)

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Message-ID: <Y8gnkm1er4XHpPvU@rowland.harvard.edu>
Date:   Wed, 18 Jan 2023 12:08:34 -0500
From:   Alan Stern <stern@...land.harvard.edu>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Andrea Parri <parri.andrea@...il.com>,
        Jonas Oberhauser <jonas.oberhauser@...wei.com>,
        Peter Zijlstra <peterz@...radead.org>, will <will@...nel.org>,
        npiggin <npiggin@...il.com>, dhowells <dhowells@...hat.com>,
        "j.alglave" <j.alglave@....ac.uk>,
        "luc.maranget" <luc.maranget@...ia.fr>, akiyks <akiyks@...il.com>,
        dlustig <dlustig@...dia.com>, joel <joel@...lfernandes.org>,
        urezki <urezki@...il.com>,
        quic_neeraju <quic_neeraju@...cinc.com>,
        frederic <frederic@...nel.org>,
        Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: Internal vs. external barriers (was: Re: Interesting LKMM litmus
 test)

On Wed, Jan 18, 2023 at 08:59:55AM -0800, Boqun Feng wrote:
> On Wed, Jan 18, 2023 at 11:03:35AM -0500, Alan Stern wrote:
> > On Tue, Jan 17, 2023 at 09:17:04PM -0800, Paul E. McKenney wrote:
> > > On Tue, Jan 17, 2023 at 09:15:15PM -0500, Alan Stern wrote:
> > > > Maybe we don't.  Please test the patch below; I think it will do what 
> > > > you want -- and it doesn't rule out nesting.
> > > 
> > > It works like a champ on manual/kernel/C-srcu*.litmus in the litmus
> > > repository on github, good show and thank you!!!
> > > 
> > > I will make more tests, and am checking this against the rest of the
> > > litmus tests in the repo, but in the meantime would you be willing to
> > > have me add your Signed-off-by?
> > 
> > I'll email a real patch submission in the not-too-distant future, 
> > assuming you don't find any problems with the new code.
> 
> I haven't tested the following, but I think we also need it to avoid
> (although rare) mixing srcu_struct with normal memory access?
> 
> Since you are working on a patch, I think I better mention this ;-)
> 
> Regards,
> Boqun
> 
> diff --git a/tools/memory-model/lock.cat b/tools/memory-model/lock.cat
> index 6b52f365d73a..c134c2027224 100644
> --- a/tools/memory-model/lock.cat
> +++ b/tools/memory-model/lock.cat
> @@ -37,7 +37,7 @@ let RU = try RU with emptyset
>  let LF = LF | RL
> 
>  (* There should be no ordinary R or W accesses to spinlocks *)
> -let ALL-LOCKS = LKR | LKW | UL | LF | RU
> +let ALL-LOCKS = LKR | LKW | UL | LF | RU | Srcu-lock | Srcu-unlock
>  flag ~empty [M \ IW] ; loc ; [ALL-LOCKS] as mixed-lock-accesses
> 
>  (* Link Lock-Reads to their RMW-partner Lock-Writes *)

Great point!  I'll at this to the patch, thanks.

Alan