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

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Message-ID: <Y8MOOrrHntA9TyUk@rowland.harvard.edu>
Date:   Sat, 14 Jan 2023 15:19:06 -0500
From:   Alan Stern <stern@...land.harvard.edu>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Jonas Oberhauser <jonas.oberhauser@...wei.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "parri.andrea" <parri.andrea@...il.com>, will <will@...nel.org>,
        "boqun.feng" <boqun.feng@...il.com>, 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 Sat, Jan 14, 2023 at 10:15:37AM -0800, Paul E. McKenney wrote:
> Nevertheless, here is the resulting .bell fragment:
> 
> ------------------------------------------------------------------------
> 
> (* Compute matching pairs of Srcu-lock and Srcu-unlock *)
> let srcu-rscs = ([Srcu-lock] ; data ; [Srcu-unlock]) & loc
> 
> (* Validate nesting *)
> flag ~empty Srcu-lock \ domain(srcu-rscs) as unbalanced-srcu-locking
> flag ~empty Srcu-unlock \ range(srcu-rscs) as unbalanced-srcu-locking
> 
> (* Check for use of synchronize_srcu() inside an RCU critical section *)
> flag ~empty rcu-rscs & (po ; [Sync-srcu] ; po) as invalid-sleep
> 
> (* Validate SRCU dynamic match *)
> flag ~empty different-values(srcu-rscs) as srcu-bad-nesting

I forgot to mention...  An appropriate check for one srcu_read_lock() 
matched to more than one srcu_read_unlock() would be something like 
this:

flag ~empty (srcu-rscs^-1 ; srcu-rscs) \ id as multiple-unlocks

Alan

PS: Do you agree that we should change the names of the first two flags 
above to unbalanced-srcu-lock and unbalanced-srcu-unlock, respectively 
(and similarly for the rcu checks)?  It might help to be a little more 
specific about how the locking is wrong when we detect an error.