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Date:   Thu, 21 Feb 2019 10:20:20 +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>,
        "David S. Miller" <davem@davemloft.net>,
        Ido Schimmel <idosch@mellanox.com>,
        Ingo Molnar <mingo@redhat.com>,
        "moderated list:INTEL ETHERNET DRIVERS" 
        <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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        Josh Triplett <josh@joshtriplett.org>, keescook@chromium.org,
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        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 5/5] rcuwait: Replace rcu_assign_pointer() with
 WRITE_ONCE
Message-ID: <20190221092020.GZ32477@hirez.programming.kicks-ass.net>
References: <20190221054942.132388-1-joel@joelfernandes.org>
 <20190221054942.132388-6-joel@joelfernandes.org>
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On Thu, Feb 21, 2019 at 12:49:42AM -0500, Joel Fernandes (Google) wrote:
> This suppresses a sparse error generated due to the recently added
> rcu_assign_pointer sparse check below. It seems WRITE_ONCE should be
> sufficient here.
> 
> >> kernel//locking/percpu-rwsem.c:162:9: sparse: error: incompatible
> types in comparison expression (different address spaces)
> 
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> ---
>  include/linux/rcuwait.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/rcuwait.h b/include/linux/rcuwait.h
> index 90bfa3279a01..9e5b4760e6c2 100644
> --- a/include/linux/rcuwait.h
> +++ b/include/linux/rcuwait.h
> @@ -44,7 +44,7 @@ extern void rcuwait_wake_up(struct rcuwait *w);
>  	 */                                                             \
>  	WARN_ON(current->exit_state);                                   \
>  									\
> -	rcu_assign_pointer((w)->task, current);				\
> +	WRITE_ONCE((w)->task, current);					\
>  	for (;;) {							\
>  		/*							\
>  		 * Implicit barrier (A) pairs with (B) in		\

Distinct lack of justification for loosing the RELEASE again.