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Commit b09e5f86 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Abstract funnel locking from synchronize_sched_expedited() 



This commit abstracts funnel locking from synchronize_sched_expedited()
so that it may be used by synchronize_rcu_expedited().

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 543c6158

kernel/rcu/tree.c

+47 −33
Original line number Diff line number Diff line
@@ -3309,16 +3309,6 @@ static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s) 
	return rcu_seq_done(&rsp->expedited_sequence, s);

}



static int synchronize_sched_expedited_cpu_stop(void *data)

{

	struct rcu_state *rsp = data;



	/* We are here: If we are last, do the wakeup. */

	if (atomic_dec_and_test(&rsp->expedited_need_qs))

		wake_up(&rsp->expedited_wq);

	return 0;

}



/* Common code for synchronize_sched_expedited() work-done checking. */

static bool sync_sched_exp_wd(struct rcu_state *rsp, struct rcu_node *rnp,

			      atomic_long_t *stat, unsigned long s)
@@ -3335,6 +3325,48 @@ static bool sync_sched_exp_wd(struct rcu_state *rsp, struct rcu_node *rnp, 
	return false;

}



/*

 * Funnel-lock acquisition for expedited grace periods.  Returns a

 * pointer to the root rcu_node structure, or NULL if some other

 * task did the expedited grace period for us.

 */

static struct rcu_node *exp_funnel_lock(struct rcu_state *rsp, unsigned long s)

{

	struct rcu_node *rnp0;

	struct rcu_node *rnp1 = NULL;



	/*

	 * Each pass through the following loop works its way

	 * up the rcu_node tree, returning if others have done the

	 * work or otherwise falls through holding the root rnp's

	 * ->exp_funnel_mutex.  The mapping from CPU to rcu_node structure

	 * can be inexact, as it is just promoting locality and is not

	 * strictly needed for correctness.

	 */

	rnp0 = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;

	for (; rnp0 != NULL; rnp0 = rnp0->parent) {

		if (sync_sched_exp_wd(rsp, rnp1, &rsp->expedited_workdone1, s))

			return NULL;

		mutex_lock(&rnp0->exp_funnel_mutex);

		if (rnp1)

			mutex_unlock(&rnp1->exp_funnel_mutex);

		rnp1 = rnp0;

	}

	if (sync_sched_exp_wd(rsp, rnp1, &rsp->expedited_workdone2, s))

		return NULL;

	return rnp1;

}



static int synchronize_sched_expedited_cpu_stop(void *data)

{

	struct rcu_state *rsp = data;



	/* We are here: If we are last, do the wakeup. */

	if (atomic_dec_and_test(&rsp->expedited_need_qs))

		wake_up(&rsp->expedited_wq);

	return 0;

}



/**

 * synchronize_sched_expedited - Brute-force RCU-sched grace period

 *
@@ -3355,8 +3387,7 @@ void synchronize_sched_expedited(void) 
{

	int cpu;

	long s;

	struct rcu_node *rnp0;

	struct rcu_node *rnp1 = NULL;

	struct rcu_node *rnp;

	struct rcu_state *rsp = &rcu_sched_state;



	/* Take a snapshot of the sequence number.  */
@@ -3370,26 +3401,9 @@ void synchronize_sched_expedited(void) 
	}

	WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));



	/*

	 * Each pass through the following loop works its way

	 * up the rcu_node tree, returning if others have done the

	 * work or otherwise falls through holding the root rnp's

	 * ->exp_funnel_mutex.  The mapping from CPU to rcu_node structure

	 * can be inexact, as it is just promoting locality and is not

	 * strictly needed for correctness.

	 */

	rnp0 = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;

	for (; rnp0 != NULL; rnp0 = rnp0->parent) {

		if (sync_sched_exp_wd(rsp, rnp1, &rsp->expedited_workdone1, s))

			return;

		mutex_lock(&rnp0->exp_funnel_mutex);

		if (rnp1)

			mutex_unlock(&rnp1->exp_funnel_mutex);

		rnp1 = rnp0;

	}

	rnp0 = rnp1;  /* rcu_get_root(rsp), AKA root rcu_node structure. */

	if (sync_sched_exp_wd(rsp, rnp0, &rsp->expedited_workdone2, s))

		return;

	rnp = exp_funnel_lock(rsp, s);

	if (rnp == NULL)

		return;  /* Someone else did our work for us. */



	rcu_exp_gp_seq_start(rsp);
@@ -3415,7 +3429,7 @@ void synchronize_sched_expedited(void) 
			   !atomic_read(&rsp->expedited_need_qs));



	rcu_exp_gp_seq_end(rsp);

	mutex_unlock(&rnp0->exp_funnel_mutex);

	mutex_unlock(&rnp->exp_funnel_mutex);

	smp_mb(); /* ensure subsequent action seen after grace period. */



	put_online_cpus();