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Message-ID: <5a494dd8d0e04030204f61067cb1010ef0c78f27.camel@perches.com>
Subject: Re: [PATCH rcu 15/18] rcu: Remove useless "ret" update in
 rcu_gp_fqs_loop()
From:   Joe Perches <joe@perches.com>
To:     "Paul E. McKenney" <paulmck@kernel.org>, rcu@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org,
        jiangshanlai@gmail.com, akpm@linux-foundation.org,
        mathieu.desnoyers@efficios.com, josh@joshtriplett.org,
        tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org,
        dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com,
        oleg@redhat.com, joel@joelfernandes.org,
        Liu Song <liu.song11@zte.com.cn>
Date:   Tue, 03 Aug 2021 09:48:23 -0700
In-Reply-To: <20210721202127.2129660-15-paulmck@kernel.org>
References: <20210721202042.GA1472052@paulmck-ThinkPad-P17-Gen-1>
         <20210721202127.2129660-15-paulmck@kernel.org>
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On Wed, 2021-07-21 at 13:21 -0700, Paul E. McKenney wrote:
> From: Liu Song <liu.song11@zte.com.cn>
> 
> Within rcu_gp_fqs_loop(), the "ret" local variable is set to the
> return value from swait_event_idle_timeout_exclusive(), but "ret" is
> unconditionally overwritten later in the code.  This commit therefore
> removes this useless assignment.
[]
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
[]
> @@ -1960,8 +1960,8 @@ static noinline_for_stack void rcu_gp_fqs_loop(void)
> ?		trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
> ?				       TPS("fqswait"));
> ?		WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS);
> -		ret = swait_event_idle_timeout_exclusive(
> -				rcu_state.gp_wq, rcu_gp_fqs_check_wake(&gf), j);
> +		(void)swait_event_idle_timeout_exclusive(rcu_state.gp_wq,
> +				 rcu_gp_fqs_check_wake(&gf), j);

It doesn't seem this is a __must_check routine so why
bother to cast to void ?

> ?		rcu_gp_torture_wait();
> ?		WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS);
> ?		/* Locking provides needed memory barriers. */