rcu/nocb: Prepare nocb_cb_wait() to start with a non-offloaded rdp
In order to be able to toggle the offloaded state from cpusets, a nocb
kthread will need to be created for all possible CPUs whenever either
of the "rcu_nocbs=" or "nohz_full=" parameters are specified.
Therefore, the nocb_cb_wait() kthread must be prepared to start running
on a de-offloaded rdp. To accomplish this, simply move the sleeping
condition to the beginning of the nocb_cb_wait() function, which prevents
this kthread from attempting to invoke callbacks before the corresponding
CPU is offloaded.
Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 8e94a53..cd596cf 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -803,6 +803,18 @@ static void nocb_cb_wait(struct rcu_data *rdp)
bool can_sleep = true;
struct rcu_node *rnp = rdp->mynode;
+ do {
+ swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
+ nocb_cb_wait_cond(rdp));
+
+ // VVV Ensure CB invocation follows _sleep test.
+ if (smp_load_acquire(&rdp->nocb_cb_sleep)) { // ^^^
+ WARN_ON(signal_pending(current));
+ trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
+ }
+ } while (!nocb_cb_can_run(rdp));
+
+
local_irq_save(flags);
rcu_momentary_dyntick_idle();
local_irq_restore(flags);
@@ -855,17 +867,6 @@ static void nocb_cb_wait(struct rcu_data *rdp)
if (needwake_state)
swake_up_one(&rdp->nocb_state_wq);
-
- do {
- swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
- nocb_cb_wait_cond(rdp));
-
- // VVV Ensure CB invocation follows _sleep test.
- if (smp_load_acquire(&rdp->nocb_cb_sleep)) { // ^^^
- WARN_ON(signal_pending(current));
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
- }
- } while (!nocb_cb_can_run(rdp));
}
/*
