On Tue, Oct 08, 2019 at 01:01:40PM +0800, Boqun Feng wrote:
> "mask_ofl_ipi" is used for iterate CPUs which IPIs are needed to send
> to, however in the IPI sending loop, "mask_ofl_ipi" along with another
> variable "mask_ofl_test" might also get modified to record which CPU's
> quiesent state can be reported by sync_rcu_exp_select_node_cpus(). Two
> variables seems to be redundant for such a propose, so this patch clean
> things a little by solely using "mask_ofl_test" for recording and
> "mask_ofl_ipi" for iteration. This would improve the readibility of the
> IPI sending loop in sync_rcu_exp_select_node_cpus().
>
> Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
> ---
Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
thanks,
- Joel
> kernel/rcu/tree_exp.h | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
> index 69c5aa64fcfd..212470018752 100644
> --- a/kernel/rcu/tree_exp.h
> +++ b/kernel/rcu/tree_exp.h
> @@ -387,10 +387,10 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
> }
> ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
> put_cpu();
> - if (!ret) {
> - mask_ofl_ipi &= ~mask;
> + /* The CPU responses the IPI, and will report QS itself */
> + if (!ret)
> continue;
> - }
> +
> /* Failed, raced with CPU hotplug operation. */
> raw_spin_lock_irqsave_rcu_node(rnp, flags);
> if ((rnp->qsmaskinitnext & mask) &&
> @@ -401,13 +401,12 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
> schedule_timeout_uninterruptible(1);
> goto retry_ipi;
> }
> - /* CPU really is offline, so we can ignore it. */
> - if (!(rnp->expmask & mask))
> - mask_ofl_ipi &= ~mask;
> + /* CPU really is offline, and we need its QS to pass GP. */
> + if (rnp->expmask & mask)
> + mask_ofl_test |= mask;
> raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> }
> /* Report quiescent states for those that went offline. */
> - mask_ofl_test |= mask_ofl_ipi;
> if (mask_ofl_test)
> rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false);
> }
> --
> 2.23.0
>
