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

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