linux-kernel - Re: [PATCH v2 1/3] locking: Document the semantics of spin_is

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Message-Id: <20180403161134.GA31898@linux.vnet.ibm.com>
Date:   Tue, 3 Apr 2018 09:11:34 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     David Howells <dhowells@...hat.com>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Andrea Parri <parri.andrea@...il.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Will Deacon <will.deacon@....com>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Akira Yokosawa <akiyks@...il.com>
Subject: Re: [PATCH v2 1/3] locking: Document the semantics of
 spin_is_locked()

On Tue, Apr 03, 2018 at 08:03:56AM -0700, Paul E. McKenney wrote:
> On Tue, Apr 03, 2018 at 04:43:00PM +0200, Peter Zijlstra wrote:
> > On Tue, Apr 03, 2018 at 07:17:18AM -0700, Paul E. McKenney wrote:
> > > Suggestions for a fix?  Clearly great care is required when using it
> > > in things like WARN_ON()...
> > 
> > Yeah, don't use it there, use lockdep_assert_held().
> 
> Good point, -ETOOEARLY.  ;-)
> 
> > As I stated before in this thread, ideally we'd make *_is_locked() go
> > away entirely.
> 
> After being reminded of the issues on UP systems, I now have much more
> sympathy for that view...

And so the main remaining use case is debug prints on !PROVE_LOCKING
builds.  Which need some thought about the UP case.

Or am I missing something here?

							Thanx, Paul