This commit adds a comment explaining why an unprotected call to
list_add() from srcu_funnel_gp_start() can be safe. TL;DR: It is only
called during very early boot when we don't have no steeking concurrency!
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
kernel/rcu/srcutree.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 39dc3015dfeba..d16104405c8f9 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -757,6 +757,12 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
rcu_seq_state(ssp->srcu_gp_seq) == SRCU_STATE_IDLE) {
WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed));
srcu_gp_start(ssp);
+
+ // And how can that list_add() in the "else" clause
+ // possibly be safe for concurrent execution? Well,
+ // it isn't. And it does not have to be. After all, it
+ // can only be executed during early boot when there is only
+ // the one boot CPU running with interrupts still disabled.
if (likely(srcu_init_done))
queue_delayed_work(rcu_gp_wq, &ssp->work,
srcu_get_delay(ssp));
--
2.31.1.189.g2e36527f23
