linux-kernel - Re: [RFC][PATCH 4/4] futex: Rewrite FUTEX_UNLOCK

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Message-ID: <20161003122349.620df91e@gandalf.local.home>
Date:   Mon, 3 Oct 2016 12:23:49 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, tglx@...utronix.de, juri.lelli@....com,
        xlpang@...hat.com, bigeasy@...utronix.de,
        linux-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com,
        jdesfossez@...icios.com, bristot@...hat.com
Subject: Re: [RFC][PATCH 4/4] futex: Rewrite FUTEX_UNLOCK_PI

On Mon, 3 Oct 2016 17:45:14 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Mon, Oct 03, 2016 at 11:36:24AM -0400, Steven Rostedt wrote:
> 
> > > +	WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount));  
> > 
> > Don't we have a rule where WARN_ON() and BUG_ON() should never have
> > "side effects"? That is, they should only check values, but their
> > contents should not update values.  
> 
> not that I'm aware, there's various places in the kernel (including
> kref.h) that relies on WARN_ON*() having side effects.

Looking more into it, I believe the "no side effect" is only with
BUG_ON(), as WARN_ON() can be used within if statements.

-- Steve