[PATCH RFC tip/core/rcu 6/7] rcu: Move early-boot callbacks to no-CBs lists for no-CBs CPUs

[Paul E. McKenney]

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

When a CPU is first determined to be a no-CBs CPUs, this commit causes
any early boot callbacks to be moved to the no-CBs callback list,
allowing them t obe invoked.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
 kernel/rcu/tree.c        |  1 +
 kernel/rcu/tree_plugin.h | 24 ++++++++++++------------
 2 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 02fa29a4d104..c5241cdd4daf 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2852,6 +2852,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
 		 * and then drop through to queue the callback.
 		 */
 		BUG_ON(cpu != -1);
+		WARN_ON_ONCE(!rcu_is_watching());
 		if (!likely(rdp->nxtlist))
 			init_default_callback_list(rdp);
 	}
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 9b7f8c8ca355..bb947ef1a2a4 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2386,18 +2386,8 @@ void __init rcu_init_nohz(void)
 		pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
 
 	for_each_rcu_flavor(rsp) {
-		for_each_cpu(cpu, rcu_nocb_mask) {
-			struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
-
-			/*
-			 * If there are early callbacks, they will need
-			 * to be moved to the nocb lists.
-			 */
-			WARN_ON_ONCE(rdp->nxttail[RCU_NEXT_TAIL] !=
-				     &rdp->nxtlist &&
-				     rdp->nxttail[RCU_NEXT_TAIL] != NULL);
-			init_nocb_callback_list(rdp);
-		}
+		for_each_cpu(cpu, rcu_nocb_mask)
+			init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu));
 		rcu_organize_nocb_kthreads(rsp);
 	}
 }
@@ -2534,6 +2524,16 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
 	if (!rcu_is_nocb_cpu(rdp->cpu))
 		return false;
 
+	/* If there are early-boot callbacks, move them to nocb lists. */
+	if (rdp->nxtlist) {
+		rdp->nocb_head = rdp->nxtlist;
+		rdp->nocb_tail = rdp->nxttail[RCU_NEXT_TAIL];
+		atomic_long_set(&rdp->nocb_q_count, rdp->qlen);
+		atomic_long_set(&rdp->nocb_q_count_lazy, rdp->qlen_lazy);
+		rdp->nxtlist = NULL;
+		rdp->qlen = 0;
+		rdp->qlen_lazy = 0;
+	}
 	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
 	return true;
 }
-- 
1.8.1.5

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