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Date:   Thu, 21 Feb 2019 10:19:44 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
        Christian Brauner <christian@brauner.io>,
        Daniel Borkmann <daniel@iogearbox.net>,
        David Ahern <dsahern@gmail.com>,
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        Ido Schimmel <idosch@mellanox.com>,
        Ingo Molnar <mingo@redhat.com>,
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        <intel-wired-lan@lists.osuosl.org>,
        Jakub Kicinski <jakub.kicinski@netronome.com>,
        Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
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        Lai Jiangshan <jiangshanlai@gmail.com>,
        Martin KaFai Lau <kafai@fb.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        netdev@vger.kernel.org, "Paul E. McKenney" <paulmck@linux.ibm.com>,
        rcu@vger.kernel.org, Song Liu <songliubraving@fb.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        xdp-newbies@vger.kernel.org, Yonghong Song <yhs@fb.com>
Subject: Re: [PATCH RFC 4/5] sched/topology: Annonate RCU pointers properly
Message-ID: <20190221091944.GY32477@hirez.programming.kicks-ass.net>
References: <20190221054942.132388-1-joel@joelfernandes.org>
 <20190221054942.132388-5-joel@joelfernandes.org>
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On Thu, Feb 21, 2019 at 12:49:41AM -0500, Joel Fernandes (Google) wrote:

> Also replace rcu_assign_pointer call on rq->sd with WRITE_ONCE. This
> should be sufficient for the rq->sd initialization.

> @@ -668,7 +668,7 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
>  
>  	rq_attach_root(rq, rd);
>  	tmp = rq->sd;
> -	rcu_assign_pointer(rq->sd, sd);
> +	WRITE_ONCE(rq->sd, sd);
>  	dirty_sched_domain_sysctl(cpu);
>  	destroy_sched_domains(tmp);

Where did the RELEASE barrier go?

That was a publish operation, now it is not.