Re: [PATCH 08/24] rcu/tree: Use static initializer for krc.lock

Paul E. McKenney
2020-05-01T21:17:06Z

On Tue, Apr 28, 2020 at 10:58:47PM +0200, Uladzislau Rezki (Sony) wrote:
> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>
> The per-CPU variable is initialized at runtime in
> kfree_rcu_batch_init(). This function is invoked before
> 'rcu_scheduler_active' is set to 'RCU_SCHEDULER_RUNNING'.
> After the initialisation, '->initialized' is to true.
>
> The raw_spin_lock is only acquired if '->initialized' is
> set to true. The worqueue item is only used if 'rcu_scheduler_active'
> set to RCU_SCHEDULER_RUNNING which happens after initialisation.
>
> Use a static initializer for krc.lock and remove the runtime
> initialisation of the lock. Since the lock can now be always
> acquired, remove the '->initialized' check.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> ---
> kernel/rcu/tree.c | 15 +++++++--------
> 1 file changed, 7 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index bc6c2bc8fa32..89e9ca3f4e3e 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2892,7 +2892,7 @@ struct kfree_rcu_cpu_work {
> * @lock: Synchronize access to this structure
> * @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES
> * @monitor_todo: Tracks whether a @monitor_work delayed work is pending
> - * @initialized: The @lock and @rcu_work fields have been initialized
> + * @initialized: The @rcu_work fields have been initialized
> *
> * This is a per-CPU structure. The reason that it is not included in
> * the rcu_data structure is to permit this code to be extracted from
> @@ -2912,7 +2912,9 @@ struct kfree_rcu_cpu {
> int count;
> };
>
> -static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc);
> +static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc) = {
> + .lock = __RAW_SPIN_LOCK_UNLOCKED(krc.lock),
> +};
>
> static __always_inline void
> debug_rcu_bhead_unqueue(struct kfree_rcu_bulk_data *bhead)
> @@ -2930,10 +2932,9 @@ krc_this_cpu_lock(unsigned long *flags)
> {
> struct kfree_rcu_cpu *krcp;
>
> - local_irq_save(*flags); // For safely calling this_cpu_ptr().
> + local_irq_save(*flags); /* For safely calling this_cpu_ptr(). */

And here as well. ;-)

Thanx, Paul

> krcp = this_cpu_ptr(&krc);
> - if (likely(krcp->initialized))
> - raw_spin_lock(&krcp->lock);
> + raw_spin_lock(&krcp->lock);
>
> return krcp;
> }
> @@ -2941,8 +2942,7 @@ krc_this_cpu_lock(unsigned long *flags)
> static inline void
> krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags)
> {
> - if (likely(krcp->initialized))
> - raw_spin_unlock(&krcp->lock);
> + raw_spin_unlock(&krcp->lock);
> local_irq_restore(flags);
> }
>
> @@ -4168,7 +4168,6 @@ static void __init kfree_rcu_batch_init(void)
> for_each_possible_cpu(cpu) {
> struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
>
> - raw_spin_lock_init(&krcp->lock);
> for (i = 0; i < KFREE_N_BATCHES; i++) {
> INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work);
> krcp->krw_arr[i].krcp = krcp;
> --
> 2.20.1
>