linux-kernel - Re: [PATCH RFC tip/core/rcu 02/16] rcu: make dead code really dead

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Message-ID: <20100415235251.GA2491@feather>
Date:	Thu, 15 Apr 2010 16:52:52 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com
Subject: Re: [PATCH RFC tip/core/rcu 02/16] rcu: make dead code really dead

On Thu, Apr 15, 2010 at 11:13:25AM -0700, Paul E. McKenney wrote:
> From: Lai Jiangshan <laijs@...fujitsu.com>
> 
> cleanup: make dead code really dead
> 
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>  kernel/rcutree.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index e54c123..6042fb8 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -1236,11 +1236,11 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
>  		break; /* grace period idle or initializing, ignore. */
>  
>  	case RCU_SAVE_DYNTICK:
> -
> -		raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
>  		if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
>  			break; /* So gcc recognizes the dead code. */

GCC's new __builtin_unreachable would help here, though obviously we
can't count on 4.5 or newer quite yet.  A wrapper in compiler.h would
let us use it when available though.

- Josh Triplett
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