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:   Fri, 12 Jul 2019 15:19:30 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Bernard Metzler <BMT@zurich.ibm.com>
Cc:     Jason Gunthorpe <jgg@ziepe.ca>, Arnd Bergmann <arnd@arndb.de>,
        Doug Ledford <dledford@redhat.com>, linux-rdma@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: Re: [PATCH] rdma/siw: avoid smp_store_mb() on a u64
Message-ID: <20190712131930.GT3419@hirez.programming.kicks-ass.net>
References: <20190712120328.GB27512@ziepe.ca>
 <20190712085212.3901785-1-arnd@arndb.de>
 <OF05C1A780.433E36D1-ON00258435.003381DA-00258435.003F847E@notes.na.collabserv.com>
 <OF36428621.B839DE8B-ON00258435.00461748-00258435.0047E413@notes.na.collabserv.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <OF36428621.B839DE8B-ON00258435.00461748-00258435.0047E413@notes.na.collabserv.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Jul 12, 2019 at 01:05:14PM +0000, Bernard Metzler wrote:
> @@ -1131,6 +1131,10 @@ int siw_poll_cq(struct ib_cq *base_cq, int num_cqe, struct ib_wc *wc)
>   *   number of not reaped CQE's regardless of its notification
>   *   type and current or new CQ notification settings.
>   *
> + * This function gets called only by kernel consumers.
> + * Notification state must immediately become visible to all
> + * associated kernel producers (QP's).

No amount of memory barriers can achieve that goal.