[tip: core/rcu] rcu/nocb: Locally accelerate callbacks as long as offloading isn't complete

[tip-bot2 for Frederic Weisbecker]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     634954c2dbf88e67aa267798f60af6b9a476cf4b
Gitweb:        https://git.kernel.org/tip/634954c2dbf88e67aa267798f60af6b9a476cf4b
Author:        Frederic Weisbecker <frederic@xxxxxxxxxx>
AuthorDate:    Fri, 13 Nov 2020 13:13:28 +01:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Wed, 06 Jan 2021 16:24:59 -08:00

rcu/nocb: Locally accelerate callbacks as long as offloading isn't complete

The local callbacks processing checks if any callbacks need acceleration.
This commit carries out this checking under nocb lock protection in
the middle of toggle operations, during which time rcu_core() executes
concurrently with GP/CB kthreads.

Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Inspired-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Tested-by: Boqun Feng <boqun.feng@xxxxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/tree.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ec14c01..03810a5 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2699,7 +2699,6 @@ static __latent_entropy void rcu_core(void)
 	unsigned long flags;
 	struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
 	struct rcu_node *rnp = rdp->mynode;
-	const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist);
 	const bool do_batch = !rcu_segcblist_completely_offloaded(&rdp->cblist);
 
 	if (cpu_is_offline(smp_processor_id()))
@@ -2720,11 +2719,11 @@ static __latent_entropy void rcu_core(void)
 
 	/* No grace period and unregistered callbacks? */
 	if (!rcu_gp_in_progress() &&
-	    rcu_segcblist_is_enabled(&rdp->cblist) && !offloaded) {
-		local_irq_save(flags);
+	    rcu_segcblist_is_enabled(&rdp->cblist) && do_batch) {
+		rcu_nocb_lock_irqsave(rdp, flags);
 		if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
 			rcu_accelerate_cbs_unlocked(rnp, rdp);
-		local_irq_restore(flags);
+		rcu_nocb_unlock_irqrestore(rdp, flags);
 	}
 
 	rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());