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

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Date:   Tue, 28 Apr 2020 22:58:47 +0200
From:   "Uladzislau Rezki (Sony)" <urezki@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Matthew Wilcox <willy@...radead.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        RCU <rcu@...r.kernel.org>, Uladzislau Rezki <urezki@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH 08/24] rcu/tree: Use static initializer for krc.lock

From: Sebastian Andrzej Siewior <bigeasy@...utronix.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@...utronix.de>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.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(). */
 	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