[PATCH rcu 10/12] rcu/tasks: Mark callbacks not currently participating in barrier operation

[neeraj . upadhyay]

From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>

Each Tasks RCU flavor keeps a count of the number of callbacks that the
current rcu_barrier_tasks*() is waiting on, but there is currently no
easy way to work out which callback is stuck.  One way to do this is to
mark idle RCU-barrier callbacks by making the ->next pointer point to
the callback itself, and this commit does just that.

Later commits will use this for debug output.

Signed-off-by: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@xxxxxxxxxx>
---
 kernel/rcu/tasks.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 127018280618..d44abcd656d6 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -283,6 +283,7 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
 			INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks);
 		if (!rtpcp->rtp_exit_list.next)
 			INIT_LIST_HEAD(&rtpcp->rtp_exit_list);
+		rtpcp->barrier_q_head.next = &rtpcp->barrier_q_head;
 		maxcpu = cpu;
 	}
 
@@ -407,6 +408,7 @@ static void rcu_barrier_tasks_generic_cb(struct rcu_head *rhp)
 	struct rcu_tasks *rtp;
 	struct rcu_tasks_percpu *rtpcp;
 
+	rhp->next = rhp; // Mark the callback as having been invoked.
 	rtpcp = container_of(rhp, struct rcu_tasks_percpu, barrier_q_head);
 	rtp = rtpcp->rtpp;
 	if (atomic_dec_and_test(&rtp->barrier_q_count))
-- 
2.40.1