linux-kernel - Re: [PATCH rcu 15/18] rcu: Remove useless "ret" update in rcu_gp_fqs

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Message-ID: <5a494dd8d0e04030204f61067cb1010ef0c78f27.camel@perches.com>
Date:   Tue, 03 Aug 2021 09:48:23 -0700
From:   Joe Perches <joe@...ches.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org,
        Liu Song <liu.song11@....com.cn>
Subject: Re: [PATCH rcu 15/18] rcu: Remove useless "ret" update in
 rcu_gp_fqs_loop()

On Wed, 2021-07-21 at 13:21 -0700, Paul E. McKenney wrote:
> From: Liu Song <liu.song11@....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. */