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

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Message-ID: <Y8gli5C/HqPRYv9Y@boqun-archlinux>
Date:   Wed, 18 Jan 2023 08:59:55 -0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Alan Stern <stern@...land.harvard.edu>
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 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 *)

> 
> Alan