linux-kernel - Re: Re: [PATCH] rdma/siw: avoid smp_store

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Message-ID: <20190712131930.GT3419@hirez.programming.kicks-ass.net>
Date:   Fri, 12 Jul 2019 15:19:30 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Bernard Metzler <BMT@...ich.ibm.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Doug Ledford <dledford@...hat.com>, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH] rdma/siw: avoid smp_store_mb() on a u64

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.