[PATCH 14/16] rcu: Locally accelerate callbacks as long as offloading isn't complete

Frederic Weisbecker
2020-10-23T14:48:21Z

The local callbacks processing checks if some callbacks need
acceleration. Keep that behaviour under nocb lock protection when
rcu_core() executes concurrently with GP/CB kthreads.

Inspired-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
---
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 45fad6977bea..4af5fed11885 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2673,7 +2673,6 @@ 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()))
@@ -2694,11 +2693,11 @@ 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());
--
2.25.1