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Date:   Thu, 3 Oct 2019 20:05:28 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     rostedt <rostedt@goodmis.org>, David Howells <dhowells@redhat.com>,
        paulmck@kernel.org, rcu <rcu@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        dipankar <dipankar@in.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Eric Dumazet <edumazet@google.com>,
        fweisbec <fweisbec@gmail.com>, Oleg Nesterov <oleg@redhat.com>,
        "Joel Fernandes, Google" <joel@joelfernandes.org>,
        Bart Van Assche <bart.vanassche@wdc.com>,
        Christoph Hellwig <hch@lst.de>, Hannes Reinecke <hare@suse.de>,
        Johannes Thumshirn <jthumshirn@suse.de>,
        Shane M Seymour <shane.seymour@hpe.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>
Subject: Re: [PATCH tip/core/rcu 1/9] rcu: Upgrade rcu_swap_protected() to
 rcu_replace()
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On Thu, Oct 03, 2019 at 12:31:38PM -0400, Mathieu Desnoyers wrote:
> We might want to consider simply using xchg() here.

As stated elsewhere, xchg() is an atomic op with full ordering, IOW it
is stupid expensive for what needs to be done.