Re: [PATCH rcu 15/18] rcu: Remove useless "ret" update in rcu_gp_fqs_loop()

[Paul E. McKenney]

On Tue, Aug 03, 2021 at 09:48:23AM -0700, Joe Perches wrote:
> On Wed, 2021-07-21 at 13:21 -0700, Paul E. McKenney wrote:
> > From: Liu Song <liu.song11@xxxxxxxxxx>
> > 
> > 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 ?

As a hint to the reader that discarding the return value is intentional
rather than an oversight.

							Thanx, Paul

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