From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v3 5/5] psi: introduce psi monitor
Date: Tue, 29 Jan 2019 16:16:49 +0100
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To: Suren Baghdasaryan <surenb@google.com>
Cc: gregkh@linuxfoundation.org, tj@kernel.org, lizefan@huawei.com, hannes@cmpxchg.org, axboe@kernel.dk, dennis@kernel.org, dennisszhou@gmail.com, mingo@redhat.com, akpm@linux-foundation.org, corbet@lwn.net, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com

On Tue, Jan 29, 2019 at 01:38:43PM +0100, Peter Zijlstra wrote:
> On Thu, Jan 24, 2019 at 01:15:18PM -0800, Suren Baghdasaryan wrote:
> > +			atomic_set(&group->polling, polling);
> > +			/*
> > +			 * Memory barrier is needed to order group->polling
> > +			 * write before times[] read in collect_percpu_times()
> > +			 */
> > +			smp_mb__after_atomic();
> 
> That's broken, smp_mb__{before,after}_atomic() can only be used on
> atomic RmW operations, something atomic_set() is _not_.

Also; the comment should explain _why_ not only what.