Re: [PATCH 09/16] rcu: Remove redundant check for online cpu

Paul E. McKenney
2014-07-23T12:21:20Z

On Wed, Jul 23, 2014 at 01:09:46AM -0400, Pranith Kumar wrote:
> There are two checks for an online CPU if two if() conditions. This commit
> simplies this by replacing it with only one check for the online CPU.
>
> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>

I admit that it is very early in the morning my time, but I don't see
this change as preserving the semantics in all cases. Please recheck
your changes to the second check.

Thanx, Paul

> ---
> kernel/rcu/tree.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 5dcbf36..8d598a2 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2602,15 +2602,18 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
> {
> bool needwake;
>
> + if (!cpu_online(smp_processor_id()))
> + return;
> +
> /*
> * If called from an extended quiescent state, invoke the RCU
> * core in order to force a re-evaluation of RCU's idleness.
> */
> - if (!rcu_is_watching() && cpu_online(smp_processor_id()))
> + if (!rcu_is_watching())
> invoke_rcu_core();
>
> - /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
> - if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
> + /* If interrupts were disabled, don't invoke RCU core. */
> + if (irqs_disabled_flags(flags))
> return;
>
> /*
> --
> 2.0.0.rc2
>