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Date:   Tue, 18 Feb 2020 12:22:26 -0800
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com,
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        edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com,
        joel@joelfernandes.org
Subject: Re: [PATCH tip/core/rcu 1/3] rcu-tasks: *_ONCE() for
 rcu_tasks_cbs_head
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On Tue, Feb 18, 2020 at 09:11:42PM +0100, Peter Zijlstra wrote:
> On Tue, Feb 18, 2020 at 08:27:19AM -0800, Paul E. McKenney wrote:
> > On Tue, Feb 18, 2020 at 08:56:48AM +0100, Peter Zijlstra wrote:
> 
> > > I just took offence at the Changelog wording. It seems to suggest there
> > > actually is a problem, there is not.
> > 
> > Quoting the changelog: "Not appropriate for backporting due to failure
> > being unlikely."
> 
> That implies there is failure, however unlikely.
> 
> In this particular case there is absolutely no failure, except perhaps
> in KCSAN. This patch is a pure annotation such that KCSAN can understand
> the code.
> 
> Like said, I don't object to the actual patch, but I do think it is
> important to call out false negatives or to describe the actual problem
> found.

I don't feel at all comfortable declaring that there is absolutely
no possibility of failure.

							Thanx, Paul