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

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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: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Uladzislau Rezki (Sony) 2022-11-29 16:58:21 +01:00 committed by Paul E. McKenney
parent 8c15a9e808
commit 8fc5494ad5
1 changed files with 4 additions and 7 deletions
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11
kernel/rcu/tree.c
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@ -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);
}
}