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

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Message-ID: <20230115051510.GG2948950@paulmck-ThinkPad-P17-Gen-1>
Date:   Sat, 14 Jan 2023 21:15:10 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Alan Stern <stern@...land.harvard.edu>
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 03:19:06PM -0500, Alan Stern wrote:
> 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

I have added this, thank you!

> 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.

I have made this change, again, thank you!

But I also added this:

flag empty srcu-rscs as no-srcu-readers

And it is always flagged.  So far, I have not found any sort of relation
that connects Srcu-lock to Srcu-unlock other than po.  I tried data,
ctrl, addr, rf, rfi, and combinations thereof.

What am I missing here?

							Thanx, Paul