[PATCH v2 07/16] rcu/tree: Use static initializer for krc.lock

Uladzislau Rezki (Sony)
2020-05-25T21:49:03Z

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.

Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
kernel/rcu/tree.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c1f4b740cf14..4b1710c1d8f6 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2868,7 +2868,7 @@ 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
* @count: Number of objects for which GP not started
*
* This is a per-CPU structure. The reason that it is not included in
@@ -2888,7 +2888,9 @@ 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)
@@ -2908,8 +2910,7 @@ krc_this_cpu_lock(unsigned long *flags)

local_irq_save(*flags); // For safely calling this_cpu_ptr().
krcp = this_cpu_ptr(&krc);
- if (likely(krcp->initialized))
- raw_spin_lock(&krcp->lock);
+ raw_spin_lock(&krcp->lock);

return krcp;
}
@@ -2917,8 +2918,7 @@ 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);
}

@@ -4141,7 +4141,6 @@ 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