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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: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Paul E. McKenney 2019-05-13 15:57:50 -07:00
parent 76c6927c3e
commit e6060b41c9
2 changed files with 3 additions and 3 deletions
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4
kernel/rcu/rcu_segcblist.c
View File

@ -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);

2
kernel/rcu/rcu_segcblist.h
View File

@ -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. */