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Subject: Re: [PATCH 1/6] MIPS: Octeon: Implement __smp_store_release()
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Paul Burton <paul.burton@imgtec.com>, linux-mips@vger.kernel.org,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Will Deacon <will@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org
References: <20210127203627.47510-1-alexander.sverdlin@nokia.com>
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From:   Alexander Sverdlin <alexander.sverdlin@nokia.com>
Message-ID: <b00f945a-1278-5fd2-321c-6ea5f07be128@nokia.com>
Date:   Thu, 28 Jan 2021 12:52:22 +0100
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Hello Peter,

On 28/01/2021 12:33, Peter Zijlstra wrote:
> This, from commit 6b07d38aaa52 ("MIPS: Octeon: Use optimized memory
> barrier primitives."):
> 
> 	#define smp_mb__before_llsc() smp_wmb()
> 	#define __smp_mb__before_llsc() __smp_wmb()
> 
> is also dodgy as hell and really wants a comment too. I'm not buying the
> Changelog of that commit either, __smp_mb__before_llsc should also
> ensure the LL cannot happen earlier, but SYNCW has no effect on loads.
> So what stops the load from being speculated?

hmm, the commit message you point to above, says:

"Since Octeon does not do speculative reads, this functions as a full barrier."

-- 
Best regards,
Alexander Sverdlin.