linux-kernel - Re: [RFC][PATCH] atomic: Fix atomic_set

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Message-ID: <5be546b5-e34a-0bce-8cf5-b7c3f7ff28fe@mellanox.com>
Date:   Fri, 9 Jun 2017 10:03:40 -0400
From:   Chris Metcalf <cmetcalf@...lanox.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, vgupta@...opsys.com,
        rkuo@...eaurora.org, james.hogan@...tec.com, jejb@...isc-linux.org,
        davem@...emloft.net
Subject: Re: [RFC][PATCH] atomic: Fix atomic_set_release() for 'funny'
 architectures

On 6/9/2017 7:05 AM, Peter Zijlstra wrote:
> Subject: atomic: Fix atomic_set_release() for 'funny' architectures
>
> Those architectures that have a special atomic_set implementation also
> need a special atomic_set_release(), because for the very same reason
> WRITE_ONCE() is broken for them, smp_store_release() is too.
>
> The vast majority is architectures that have spinlock hash based atomic
> implementation except hexagon which seems to have a hardware 'feature'.
>
> The spinlock based atomics should be SC, that is, none of them appear to
> place extra barriers in atomic_cmpxchg() or any of the other SC atomic
> primitives and therefore seem to rely on their spinlock implementation
> being SC (I did not fully validate all that).
>
> Therefore, the normal atomic_set() is SC and can be used at
> atomic_set_release().

Acked-by: Chris Metcalf <cmetcalf@...lanox.com> [for tile]

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com