Commit c63eb17f authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Create call_rcu_tasks() kthread at boot time 



Currently the call_rcu_tasks() kthread is created upon first
invocation of call_rcu_tasks().  This has the advantage of avoiding
creation if there are never any invocations of call_rcu_tasks() and of
synchronize_rcu_tasks(), but it requires an unreliable heuristic to
determine when it is safe to create the kthread.  For example, it is
not safe to create the kthread when call_rcu_tasks() is invoked with
a spinlock held, but there is no good way to detect this in !PREEMPT
kernels.

This commit therefore creates this kthread unconditionally at
core_initcall() time.  If you don't want this kthread created, then
build with CONFIG_TASKS_RCU=n.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 135bd1a2

kernel/rcu/update.c

+5 −19
Original line number Diff line number Diff line
@@ -575,7 +575,6 @@ DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu); 
static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT;

module_param(rcu_task_stall_timeout, int, 0644);



static void rcu_spawn_tasks_kthread(void);

static struct task_struct *rcu_tasks_kthread_ptr;



/**
@@ -600,7 +599,6 @@ void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func) 
{

	unsigned long flags;

	bool needwake;

	bool havetask = READ_ONCE(rcu_tasks_kthread_ptr);



	rhp->next = NULL;

	rhp->func = func;
@@ -610,12 +608,9 @@ void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func) 
	rcu_tasks_cbs_tail = &rhp->next;

	raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);

	/* We can't create the thread unless interrupts are enabled. */

	if ((needwake && havetask) ||

	    (!havetask && !irqs_disabled_flags(flags))) {

		rcu_spawn_tasks_kthread();

	if (needwake && READ_ONCE(rcu_tasks_kthread_ptr))

		wake_up(&rcu_tasks_cbs_wq);

}

}

EXPORT_SYMBOL_GPL(call_rcu_tasks);



/**
@@ -853,27 +848,18 @@ static int __noreturn rcu_tasks_kthread(void *arg) 
	}

}



/* Spawn rcu_tasks_kthread() at first call to call_rcu_tasks(). */

static void rcu_spawn_tasks_kthread(void)

/* Spawn rcu_tasks_kthread() at core_initcall() time. */

static int __init rcu_spawn_tasks_kthread(void)

{

	static DEFINE_MUTEX(rcu_tasks_kthread_mutex);

	struct task_struct *t;



	if (READ_ONCE(rcu_tasks_kthread_ptr)) {

		smp_mb(); /* Ensure caller sees full kthread. */

		return;

	}

	mutex_lock(&rcu_tasks_kthread_mutex);

	if (rcu_tasks_kthread_ptr) {

		mutex_unlock(&rcu_tasks_kthread_mutex);

		return;

	}

	t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread");

	BUG_ON(IS_ERR(t));

	smp_mb(); /* Ensure others see full kthread. */

	WRITE_ONCE(rcu_tasks_kthread_ptr, t);

	mutex_unlock(&rcu_tasks_kthread_mutex);

	return 0;

}

core_initcall(rcu_spawn_tasks_kthread);



/* Do the srcu_read_lock() for the above synchronize_srcu().  */

void exit_tasks_rcu_start(void)

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