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Date:   Wed, 26 Feb 2020 09:58:12 -0500 (EST)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Boqun Feng <boqun.feng@gmail.com>
cc:     linux-kernel@vger.kernel.org, <rcu@vger.kernel.org>,
        Andrea Parri <parri.andrea@gmail.com>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        David Howells <dhowells@redhat.com>,
        Jade Alglave <j.alglave@ucl.ac.uk>,
        Luc Maranget <luc.maranget@inria.fr>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Akira Yokosawa <akiyks@gmail.com>,
        Daniel Lustig <dlustig@nvidia.com>,
        <linux-arch@vger.kernel.org>
Subject: Re: [PATCH] tools/memory-model: Remove lock-final checking in lock.cat
In-Reply-To: <20200226032142.89424-1-boqun.feng@gmail.com>
Message-ID: <Pine.LNX.4.44L0.2002260953110.3674-100000@netrider.rowland.org>
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On Wed, 26 Feb 2020, Boqun Feng wrote:

> In commit 30b795df11a1 ("tools/memory-model: Improve mixed-access
> checking in lock.cat"), we have added the checking to disallow any
> normal memory access to lock variables, and this checking is stronger
> than lock-final. So remove the lock-final checking as it's unnecessary
> now.

I don't understand this description.  Why do you say that the
normal-access checking is stronger than the lock-final check?

> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> ---
>  tools/memory-model/lock.cat | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/tools/memory-model/lock.cat b/tools/memory-model/lock.cat
> index 6b52f365d73a..827a3646607c 100644
> --- a/tools/memory-model/lock.cat
> +++ b/tools/memory-model/lock.cat
> @@ -54,9 +54,6 @@ flag ~empty LKR \ domain(lk-rmw) as unpaired-LKR
>   *)
>  empty ([LKW] ; po-loc ; [LKR]) \ (po-loc ; [UL] ; po-loc) as lock-nest
>  
> -(* The final value of a spinlock should not be tested *)
> -flag ~empty [FW] ; loc ; [ALL-LOCKS] as lock-final
> -
>  (*
>   * Put lock operations in their appropriate classes, but leave UL out of W
>   * until after the co relation has been generated.

With this check removed, what will prevent people from writing litmus 
tests like this?

C test

{
	spinlock_t s;
}

...

exists (s=0)

Alan