Commit 8fc5494a authored by Uladzislau Rezki (Sony)'s avatar Uladzislau Rezki (Sony) Committed by Paul E. McKenney
Browse files

rcu/kvfree: Move need_offload_krc() out of krcp->lock 



The need_offload_krc() function currently holds the krcp->lock in order
to safely check krcp->head.  This commit removes the need for this lock
in that function by updating the krcp->head pointer using WRITE_ONCE()
macro so that readers can carry out lockless loads of that pointer.

Signed-off-by: default avatarUladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 8c15a9e8

kernel/rcu/tree.c

+4 −7
Original line number Diff line number Diff line
@@ -3194,7 +3194,7 @@ static void kfree_rcu_monitor(struct work_struct *work) 
			// objects queued on the linked list.

			if (!krwp->head_free) {

				krwp->head_free = krcp->head;

				krcp->head = NULL;

				WRITE_ONCE(krcp->head, NULL);

			}



			WRITE_ONCE(krcp->count, 0);
@@ -3208,6 +3208,8 @@ static void kfree_rcu_monitor(struct work_struct *work) 
		}

	}



	raw_spin_unlock_irqrestore(&krcp->lock, flags);



	// If there is nothing to detach, it means that our job is

	// successfully done here. In case of having at least one

	// of the channels that is still busy we should rearm the
@@ -3215,8 +3217,6 @@ static void kfree_rcu_monitor(struct work_struct *work) 
	// still in progress.

	if (need_offload_krc(krcp))

		schedule_delayed_monitor_work(krcp);



	raw_spin_unlock_irqrestore(&krcp->lock, flags);

}



static enum hrtimer_restart
@@ -3386,7 +3386,7 @@ void kvfree_call_rcu(struct rcu_head *head, void *ptr) 


		head->func = ptr;

		head->next = krcp->head;

		krcp->head = head;

		WRITE_ONCE(krcp->head, head);

		success = true;

	}
@@ -3463,15 +3463,12 @@ static struct shrinker kfree_rcu_shrinker = { 
void __init kfree_rcu_scheduler_running(void)

{

	int cpu;

	unsigned long flags;



	for_each_possible_cpu(cpu) {

		struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);



		raw_spin_lock_irqsave(&krcp->lock, flags);

		if (need_offload_krc(krcp))

			schedule_delayed_monitor_work(krcp);

		raw_spin_unlock_irqrestore(&krcp->lock, flags);

	}

}