Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 30 Apr 2019 10:34:09 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Andrea Parri <andrea.parri@amarulasolutions.com>
Cc:     linux-kernel@vger.kernel.org,
        "Paul E. McKenney" <paulmck@linux.ibm.com>,
        Rob Clark <robdclark@gmail.com>, Sean Paul <sean@poorly.run>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Jordan Crouse <jcrouse@codeaurora.org>,
        Jens Axboe <axboe@kernel.dk>, Omar Sandoval <osandov@fb.com>,
        "Yan, Zheng" <zyan@redhat.com>, Sage Weil <sage@redhat.com>,
        Ilya Dryomov <idryomov@gmail.com>,
        Dennis Dalessandro <dennis.dalessandro@intel.com>,
        Mike Marciniszyn <mike.marciniszyn@intel.com>,
        Doug Ledford <dledford@redhat.com>,
        Jason Gunthorpe <jgg@ziepe.ca>
Subject: Re: [PATCH 0/5] Fix improper uses of smp_mb__{before,after}_atomic()
Message-ID: <20190430083409.GD2677@hirez.programming.kicks-ass.net>
References: <1556568902-12464-1-git-send-email-andrea.parri@amarulasolutions.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1556568902-12464-1-git-send-email-andrea.parri@amarulasolutions.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Apr 29, 2019 at 10:14:56PM +0200, Andrea Parri wrote:
> Hello!
> 
> A relatively common misuse of these barriers is to apply these to
> operations which are not read-modify-write operations, such as
> atomic_set() and atomic_read(); examples were discussed in [1].
> 
> This series attempts to fix those uses by (conservatively) replacing
> the smp_mb__{before,after}_atomic() barriers with full memory barriers.

I don't think blindly doing this replacement makes the code any better;
much of the code you found is just straight up dodgy to begin with.

I think the people should mostly just consider this a bug report.

Also, remember a memory barrier without a coherent comment is most
likely a bug anyway.