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rcu: Make kfree_rcu() use a non-atomic ->monitor_todo

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Because the ->monitor_todo field is always protected by krcp->lock,
this commit downgrades from xchg() to non-atomic unmarked assignment
statements.

Signed-off-by: Joel Fernandes <joel@joelfernandes.org>
[ paulmck: Update to include early-boot kick code. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Joel Fernandes 2019-09-22 10:49:57 -07:00 committed by Paul E. McKenney
parent e6e78b004f
commit 569d767087
1 changed files with 10 additions and 6 deletions
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16
kernel/rcu/tree.c
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@ -2708,7 +2708,7 @@ struct kfree_rcu_cpu {
struct rcu_head *head_free;
spinlock_t lock;
struct delayed_work monitor_work;
int monitor_todo;
bool monitor_todo;
bool initialized;
};
@ -2765,6 +2765,7 @@ static inline void kfree_rcu_drain_unlock(struct kfree_rcu_cpu *krcp,
unsigned long flags)
{
// Attempt to start a new batch.
krcp->monitor_todo = false;
if (queue_kfree_rcu_work(krcp)) {
// Success! Our job is done here.
spin_unlock_irqrestore(&krcp->lock, flags);
@ -2772,8 +2773,8 @@ static inline void kfree_rcu_drain_unlock(struct kfree_rcu_cpu *krcp,
}
// Previous RCU batch still in progress, try again later.
if (!xchg(&krcp->monitor_todo, true))
schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
krcp->monitor_todo = true;
schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
spin_unlock_irqrestore(&krcp->lock, flags);
}
@ -2788,7 +2789,7 @@ static void kfree_rcu_monitor(struct work_struct *work)
monitor_work.work);
spin_lock_irqsave(&krcp->lock, flags);
if (xchg(&krcp->monitor_todo, false))
if (krcp->monitor_todo)
kfree_rcu_drain_unlock(krcp, flags);
else
spin_unlock_irqrestore(&krcp->lock, flags);
@ -2837,8 +2838,10 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
// Set timer to drain after KFREE_DRAIN_JIFFIES.
if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
!xchg(&krcp->monitor_todo, true))
!krcp->monitor_todo) {
krcp->monitor_todo = true;
schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
}
if (krcp->initialized)
spin_unlock(&krcp->lock);
@ -2855,10 +2858,11 @@ void __init kfree_rcu_scheduler_running(void)
struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
spin_lock_irqsave(&krcp->lock, flags);
if (!krcp->head || xchg(&krcp->monitor_todo, true)) {
if (!krcp->head || krcp->monitor_todo) {
spin_unlock_irqrestore(&krcp->lock, flags);
continue;
}
krcp->monitor_todo = true;
schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
spin_unlock_irqrestore(&krcp->lock, flags);
}