When the boot CPU initializes the per-CPU data on behalf of all possible
CPUs, a sanity check is performed on each of them to make sure none is
initialized in an extended quiescent state.

This check involves a full memory barrier which is useless at this early
boot stage.

Do a plain access instead.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 kernel/rcu/tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f5354de5644b..02f6f3483482 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4812,7 +4812,7 @@ rcu_boot_init_percpu_data(int cpu)
 	rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
 	INIT_WORK(&rdp->strict_work, strict_work_handler);
 	WARN_ON_ONCE(ct->dynticks_nesting != 1);
-	WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu)));
+	WARN_ON_ONCE(rcu_dynticks_in_eqs(ct_dynticks_cpu(cpu)));
 	rdp->barrier_seq_snap = rcu_state.barrier_sequence;
 	rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
 	rdp->rcu_ofl_gp_state = RCU_GP_CLEANED;
-- 
2.44.0

On 15/05/24 14:53, Frederic Weisbecker wrote:
> When the boot CPU initializes the per-CPU data on behalf of all possible
> CPUs, a sanity check is performed on each of them to make sure none is
> initialized in an extended quiescent state.
>
> This check involves a full memory barrier which is useless at this early
> boot stage.
>
> Do a plain access instead.
>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

Reviewed-by: Valentin Schneider <vschneid@redhat.com>