[PATCH rcu 2/3] srcu: Update cleanup_srcu_struct() comment

["Paul E. McKenney" <paulmck@kernel.org>]

Now that we have polled SRCU grace periods, a grace period can be
started by start_poll_synchronize_srcu() as well as call_srcu(),
synchronize_srcu(), and synchronize_srcu_expedited().  This commit
therefore calls out this new start_poll_synchronize_srcu() possibility
in the comment on the WARN_ON().

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/srcutree.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index bc4b58b0204e9..15dc22a8ff5ab 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -667,7 +667,10 @@ void cleanup_srcu_struct(struct srcu_struct *ssp)
 		pr_info("%s: Active srcu_struct %p read state: %d gp state: %lu/%lu\n",
 			__func__, ssp, rcu_seq_state(READ_ONCE(sup->srcu_gp_seq)),
 			rcu_seq_current(&sup->srcu_gp_seq), sup->srcu_gp_seq_needed);
-		return; /* Caller forgot to stop doing call_srcu()? */
+		return; // Caller forgot to stop doing call_srcu()?
+			// Or caller invoked start_poll_synchronize_srcu()
+			// and then cleanup_srcu_struct() before that grace
+			// period ended?
 	}
 	kfree(sup->node);
 	sup->node = NULL;
-- 
2.40.1