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rcu-tasks: Use rcuwait for the rcu_tasks_kthread() 

The waitqueue used by rcu_tasks_kthread() has always only one waiter.
With a guaranteed only one waiter, this can be replaced with rcuwait
which is smaller and simpler. With rcuwait based wake counterpart, the
irqwork function (call_rcu_tasks_iw_wakeup()) can be invoked hardirq
context because it is only a wake up and no sleeping locks are involved
(unlike the wait_queue_head).
As a side effect, this is also one piece of the puzzle to pass the RCU
selftest at early boot on PREEMPT_RT.

Replace wait_queue_head with rcuwait and let the irqwork run in hardirq
context on PREEMPT_RT.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Sebastian Andrzej Siewior 2022-03-04 12:07:25 +01:00 committed by Paul E. McKenney
parent f25390033f
commit 88db792bbe
1 changed files with 8 additions and 6 deletions
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14
kernel/rcu/tasks.h
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@ -46,7 +46,7 @@ struct rcu_tasks_percpu {
/**
* struct rcu_tasks - Definition for a Tasks-RCU-like mechanism.
* @cbs_wq: Wait queue allowing new callback to get kthread's attention.
* @cbs_wait: RCU wait allowing a new callback to get kthread's attention.
* @cbs_gbl_lock: Lock protecting callback list.
* @kthread_ptr: This flavor's grace-period/callback-invocation kthread.
* @gp_func: This flavor's grace-period-wait function.
@ -77,7 +77,7 @@ struct rcu_tasks_percpu {
* @kname: This flavor's kthread name.
*/
struct rcu_tasks {
struct wait_queue_head cbs_wq;
struct rcuwait cbs_wait;
raw_spinlock_t cbs_gbl_lock;
int gp_state;
int gp_sleep;
@ -113,11 +113,11 @@ static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp);
#define DEFINE_RCU_TASKS(rt_name, gp, call, n) \
static DEFINE_PER_CPU(struct rcu_tasks_percpu, rt_name ## __percpu) = { \
.lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name ## __percpu.cbs_pcpu_lock), \
.rtp_irq_work = IRQ_WORK_INIT(call_rcu_tasks_iw_wakeup), \
.rtp_irq_work = IRQ_WORK_INIT_HARD(call_rcu_tasks_iw_wakeup), \
}; \
static struct rcu_tasks rt_name = \
{ \
.cbs_wq = __WAIT_QUEUE_HEAD_INITIALIZER(rt_name.cbs_wq), \
.cbs_wait = __RCUWAIT_INITIALIZER(rt_name.wait), \
.cbs_gbl_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_gbl_lock), \
.gp_func = gp, \
.call_func = call, \
@ -266,7 +266,7 @@ static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp)
struct rcu_tasks_percpu *rtpcp = container_of(iwp, struct rcu_tasks_percpu, rtp_irq_work);
rtp = rtpcp->rtpp;
wake_up(&rtp->cbs_wq);
rcuwait_wake_up(&rtp->cbs_wait);
}
// Enqueue a callback for the specified flavor of Tasks RCU.
@ -514,7 +514,9 @@ static int __noreturn rcu_tasks_kthread(void *arg)
set_tasks_gp_state(rtp, RTGS_WAIT_CBS);
/* If there were none, wait a bit and start over. */
wait_event_idle(rtp->cbs_wq, (needgpcb = rcu_tasks_need_gpcb(rtp)));
rcuwait_wait_event(&rtp->cbs_wait,
(needgpcb = rcu_tasks_need_gpcb(rtp)),
TASK_IDLE);
if (needgpcb & 0x2) {
// Wait for one grace period.