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Date:   Fri, 28 Aug 2020 09:34:10 +0800
From:   Boqun Feng <boqun.feng@gmail.com>
To:     Cameron <cameron@moodycamel.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org, mhiramat@kernel.org,
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        anil.s.keshavamurthy@intel.com, linux-arch@vger.kernel.org,
        oleg@redhat.com, will@kernel.org, paulmck@kernel.org
Subject: Re: [RFC][PATCH 6/7] freelist: Lock less freelist
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On Thu, Aug 27, 2020 at 03:57:22PM -0400, Cameron wrote:
> On Thu, Aug 27, 2020 at 3:08 PM Boqun Feng <boqun.feng@gmail.com> wrote:
> > So if try_cmpxchg_acquire() fails, we don't have ACQUIRE semantics on
> > read of the new list->head, right? Then probably a
> > smp_mb__after_atomic() is needed in that case?
> 
> Yes, there needs to be an acquire on the head after a failed cmpxchg;
> does the atomic_fetch_add following that not have acquire semantics?
> 

Yes, you're right, the atomic_fecth_add() following is a fully-ordered
atomic, so could provide the necessary ACQUIRE semantics. I was missing
that. Maybe a few words explaining this helps.

Regards,
Boqun

> Cameron