linux-kernel - Re: [PATCH] locking/osq_lock: fix a data race in osq_wait

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Message-ID: <20200129184935.GU14879@hirez.programming.kicks-ass.net>
Date:   Wed, 29 Jan 2020 19:49:35 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Marco Elver <elver@...gle.com>, Qian Cai <cai@....pw>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH] locking/osq_lock: fix a data race in osq_wait_next

On Tue, Jan 28, 2020 at 04:22:53PM -0800, Paul E. McKenney wrote:
> On Tue, Jan 28, 2020 at 05:56:55PM +0100, Peter Zijlstra wrote:
> > On Tue, Jan 28, 2020 at 12:46:26PM +0100, Marco Elver wrote:
> > 
> > > > Marco, any thought on improving KCSAN for this to reduce the false
> > > > positives?
> > > 
> > > Define 'false positive'.
> > 
> > I'll use it where the code as written is correct while the tool
> > complains about it.
> 
> I could be wrong, but I would guess that Marco is looking for something
> a little less subjective and a little more specific.  ;-)

How is that either? If any valid translation by a compile results in
correct functionality, yet the tool complains, then surely we can speak
of a objective fact.