Commit e6060b41 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu/nocb: Allow lockless use of rcu_segcblist_empty() 



Currently, rcu_segcblist_empty() assumes that the callback list is not
being changed by other CPUs, but upcoming changes will require it to
operate locklessly.  This commit therefore adds the needed READ_ONCE()
call, along with the WRITE_ONCE() calls when updating the callback list's
->head field.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.ibm.com>
parent 76c6927c

kernel/rcu/rcu_segcblist.c

+2 −2
Original line number Diff line number Diff line
@@ -213,7 +213,7 @@ void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp, 
	if (!rcu_segcblist_ready_cbs(rsclp))

		return; /* Nothing to do. */

	*rclp->tail = rsclp->head;

	rsclp->head = *rsclp->tails[RCU_DONE_TAIL];

	WRITE_ONCE(rsclp->head, *rsclp->tails[RCU_DONE_TAIL]);

	WRITE_ONCE(*rsclp->tails[RCU_DONE_TAIL], NULL);

	rclp->tail = rsclp->tails[RCU_DONE_TAIL];

	for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--)
@@ -268,7 +268,7 @@ void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp, 
	if (!rclp->head)

		return; /* No callbacks to move. */

	*rclp->tail = rsclp->head;

	rsclp->head = rclp->head;

	WRITE_ONCE(rsclp->head, rclp->head);

	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++)

		if (&rsclp->head == rsclp->tails[i])

			WRITE_ONCE(rsclp->tails[i], rclp->tail);

kernel/rcu/rcu_segcblist.h

+1 −1
Original line number Diff line number Diff line
@@ -36,7 +36,7 @@ struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp); 
 */

static inline bool rcu_segcblist_empty(struct rcu_segcblist *rsclp)

{

	return !rsclp->head;

	return !READ_ONCE(rsclp->head);

}



/* Return number of callbacks in segmented callback list. */

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