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Commit c91a8675 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Add accessor macros for the ->need_future_gp[] array 



Accessors for the ->need_future_gp[] array are currently open-coded,
which makes them difficult to change.  To improve maintainability, this
commit adds need_future_gp_mask() to compute the indexing mask from the
array size, need_future_gp_element() to access the element corresponding
to the specified grace-period number, and need_any_future_gp() to
determine if any future grace period is needed.  This commit also applies
need_future_gp_element() to existing open-coded single-element accesses.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: default avatarNicholas Piggin <npiggin@gmail.com>
parent 825a9911

kernel/rcu/tree.c

+7 −9
Original line number Diff line number Diff line
@@ -718,11 +718,9 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp) 
static int rcu_future_needs_gp(struct rcu_state *rsp)

{

	struct rcu_node *rnp = rcu_get_root(rsp);

	int idx = (READ_ONCE(rnp->completed) + 1) & 0x1;

	int *fp = &rnp->need_future_gp[idx];



	lockdep_assert_irqs_disabled();

	return READ_ONCE(*fp);

	return READ_ONCE(need_future_gp_element(rnp, rnp->completed));

}



/*
@@ -1699,7 +1697,7 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp, 
	 */

	c = rcu_cbs_completed(rdp->rsp, rnp);

	trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));

	if (rnp->need_future_gp[c & 0x1]) {

	if (need_future_gp_element(rnp, c)) {

		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));

		goto out;

	}
@@ -1711,7 +1709,7 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp, 
	 * current grace period, we don't need to explicitly start one.

	 */

	if (rnp->gpnum != rnp->completed) {

		rnp->need_future_gp[c & 0x1]++;

		need_future_gp_element(rnp, c)++;

		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));

		goto out;

	}
@@ -1737,13 +1735,13 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp, 
	 * If the needed for the required grace period is already

	 * recorded, trace and leave.

	 */

	if (rnp_root->need_future_gp[c & 0x1]) {

	if (need_future_gp_element(rnp_root, c)) {

		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));

		goto unlock_out;

	}



	/* Record the need for the future grace period. */

	rnp_root->need_future_gp[c & 0x1]++;

	need_future_gp_element(rnp_root, c)++;



	/* If a grace period is not already in progress, start one. */

	if (rnp_root->gpnum != rnp_root->completed) {
@@ -1771,8 +1769,8 @@ static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) 
	int needmore;

	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);



	rnp->need_future_gp[c & 0x1] = 0;

	needmore = rnp->need_future_gp[(c + 1) & 0x1];

	need_future_gp_element(rnp, c) = 0;

	needmore = need_future_gp_element(rnp, c + 1);

	trace_rcu_future_gp(rnp, rdp, c,

			    needmore ? TPS("CleanupMore") : TPS("Cleanup"));

	return needmore;

kernel/rcu/tree.h

+15 −0
Original line number Diff line number Diff line
@@ -159,6 +159,21 @@ struct rcu_node { 
	wait_queue_head_t exp_wq[4];

} ____cacheline_internodealigned_in_smp;



/* Accessors for ->need_future_gp[] array. */

#define need_future_gp_mask() \

	(ARRAY_SIZE(((struct rcu_node *)NULL)->need_future_gp) - 1)

#define need_future_gp_element(rnp, c) \

	((rnp)->need_future_gp[(c) & need_future_gp_mask()])

#define need_any_future_gp(rnp)						\

({									\

	int __i;							\

	bool __nonzero = false;						\

									\

	for (__i = 0; __i < ARRAY_SIZE((rnp)->need_future_gp); __i++)	\

		__nonzero = __nonzero || (rnp)->need_future_gp[__i];	\

	__nonzero;							\

})



/*

 * Bitmasks in an rcu_node cover the interval [grplo, grphi] of CPU IDs, and

 * are indexed relative to this interval rather than the global CPU ID space.

kernel/rcu/tree_plugin.h

+1 −1
Original line number Diff line number Diff line
@@ -1790,7 +1790,7 @@ static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq) 
 */

static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)

{

	rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;

	need_future_gp_element(rnp, rnp->completed + 1) += nrq;

}



static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)