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Date:   Tue, 20 Dec 2022 23:57:56 +0100
From:   Frederic Weisbecker <frederic@kernel.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Joel Fernandes <joel@joelfernandes.org>,
        linux-kernel@vger.kernel.org,
        Josh Triplett <josh@joshtriplett.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        "Paul E. McKenney" <paulmck@kernel.org>, rcu@vger.kernel.org,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [RFC 0/2] srcu: Remove pre-flip memory barrier
Message-ID: <20221220225756.GB26563@lothringen>
References: <6438d903-ab97-48c7-c338-9f0bc2686f94@efficios.com>
 <7A9876BA-C375-42A7-A5C9-FD940D2898D7@joelfernandes.org>
 <5bd5ee4a-710a-96bc-abe8-772b2e60f478@efficios.com>
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On Tue, Dec 20, 2022 at 02:01:30PM -0500, Mathieu Desnoyers wrote:
> On 2022-12-20 13:29, Joel Fernandes wrote:
> > 
> 
> > I do want to finish my memory barrier studies of SRCU over the holidays since I have been deep in the hole with that already. Back to the post flip memory barrier here since I think now even that might not be needed…
> 
> I strongly suspect the memory barrier after flip is useless for the same
> reasons I mentioned explaining why the barrier before the flip is useless.
> 
> However, we need to double-check that we have memory barriers at the
> beginning and end of synchronize_srcu, and between load of "unlock" counters
> and load of "lock" counters.
> 
> Where is the barrier at the beginning of synchronize_srcu ?

rcu_seq_snap() ?

> 
> Thanks,
> 
> Mathieu
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com
>