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Date: Tue, 3 Apr 2018 07:17:18 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: David Howells <dhowells@redhat.com>
Cc: Andrea Parri <andrea.parri@amarulasolutions.com>,
        Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
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        Will Deacon <will.deacon@arm.com>, Boqun Feng <boqun.feng@gmail.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        Jade Alglave <j.alglave@ucl.ac.uk>,
        Luc Maranget <luc.maranget@inria.fr>,
        Akira Yokosawa <akiyks@gmail.com>
Subject: Re: [PATCH v2 1/3] locking: Document the semantics of
 spin_is_locked()
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On Tue, Apr 03, 2018 at 02:52:33PM +0100, David Howells wrote:
> Andrea Parri <andrea.parri@amarulasolutions.com> wrote:
> 
> > > It's more complicated than that.  This function is dangerous and should be
> > > used with extreme care.  In the case where CONFIG_SMP=n the value is locked
> > > one way or the other and it might be the wrong way.
> > 
> > You mean "unlocked"? (aka, return 0)
> 
> No, I mean "fixed", sorry.  We've had problems stemming from this before on UP
> systems.

Oooh...  I had forgotten about spinlocks disappearing on UP systems,
good catch!

Suggestions for a fix?  Clearly great care is required when using it
in things like WARN_ON()...

							Thanx, Paul