On Wed, Aug 17, 2022 at 09:42:52AM +0800, Zhen Lei wrote:
> 'rcu_state.nocb_is_setup' is initialized to true only if 'rcu_nocb_mask'
> successfully allocates memory. So it can be replaced by
> 'cpumask_available(rcu_nocb_mask)'. More importantly, the latter is more
> intuitive, and it has been used in several places.
>
> Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
One of the implementations of cpumask_available() does indeed check
for NULL. But here is the other one:
static inline bool cpumask_available(cpumask_var_t mask)
{
return true;
}
So I have to ask... In a kernel built with CONFIG_CPUMASK_OFFSTACK=n,
will this change really work?
Another important question is "Do all of the existing uses of
cpumask_available() really work?" Yes, I do believe that they do
work, but it would be good to get another set of eyes on that code.
"All software developers are blind!" ;-)
Thanx, Paul
> ---
> kernel/rcu/tree.h | 1 -
> kernel/rcu/tree_nocb.h | 8 +++-----
> 2 files changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> index d4a97e40ea9c3e2..06f659c63d2d192 100644
> --- a/kernel/rcu/tree.h
> +++ b/kernel/rcu/tree.h
> @@ -375,7 +375,6 @@ struct rcu_state {
> arch_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
> /* Synchronize offline with */
> /* GP pre-initialization. */
> - int nocb_is_setup; /* nocb is setup from boot */
> };
>
> /* Values for rcu_state structure's gp_flags field. */
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> index 0a5f0ef41484518..ff763e7dc53551f 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -69,7 +69,6 @@ static int __init rcu_nocb_setup(char *str)
> cpumask_setall(rcu_nocb_mask);
> }
> }
> - rcu_state.nocb_is_setup = true;
> return 1;
> }
> __setup("rcu_nocbs", rcu_nocb_setup);
> @@ -1215,7 +1214,7 @@ void __init rcu_init_nohz(void)
> struct rcu_data *rdp;
>
> #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
> - if (!rcu_state.nocb_is_setup) {
> + if (!cpumask_available(rcu_nocb_mask)) {
> need_rcu_nocb_mask = true;
> offload_all = true;
> }
> @@ -1235,10 +1234,9 @@ void __init rcu_init_nohz(void)
> return;
> }
> }
> - rcu_state.nocb_is_setup = true;
> }
>
> - if (!rcu_state.nocb_is_setup)
> + if (!cpumask_available(rcu_nocb_mask))
> return;
>
> #if defined(CONFIG_NO_HZ_FULL)
> @@ -1299,7 +1297,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
> struct task_struct *t;
> struct sched_param sp;
>
> - if (!rcu_scheduler_fully_active || !rcu_state.nocb_is_setup)
> + if (!rcu_scheduler_fully_active || !cpumask_available(rcu_nocb_mask))
> return;
>
> /* If there already is an rcuo kthread, then nothing to do. */
> --
> 2.25.1
>
