linux-kernel - Re: Some -serious- BPF-related litmus tests

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Message-ID: <20200522143201.GB32434@rowland.harvard.edu>
Date:   Fri, 22 May 2020 10:32:01 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>, parri.andrea@...il.com,
        will@...nel.org, boqun.feng@...il.com, npiggin@...il.com,
        dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr,
        akiyks@...il.com, dlustig@...dia.com, joel@...lfernandes.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        andriin@...com
Subject: Re: Some -serious- BPF-related litmus tests

On Fri, May 22, 2020 at 11:44:07AM +0200, Peter Zijlstra wrote:
> On Thu, May 21, 2020 at 05:38:50PM -0700, Paul E. McKenney wrote:
> > Hello!
> > 
> > Just wanted to call your attention to some pretty cool and pretty serious
> > litmus tests that Andrii did as part of his BPF ring-buffer work:
> > 
> > https://lore.kernel.org/bpf/20200517195727.279322-3-andriin@fb.com/
> > 
> > Thoughts?
> 
> I find:
> 
> 	smp_wmb()
> 	smp_store_release()
> 
> a _very_ weird construct. What is that supposed to even do?

Indeed, it looks like one or the other of those is redundant (depending 
on the context).

Also, what use is a spinlock that is accessed in only one thread?

Finally, I doubt that these tests belong under tools/memory-model.  
Shouldn't they go under the new Documentation/ directory for litmus 
tests?  And shouldn't the patch update a README file?

Alan