linux-kernel - [PATCH 6/6] rcu: Add comment to rcu_do_batch() identifying rcuoc code path

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Date:   Wed, 15 Mar 2023 19:38:51 +0000
From:   "Joel Fernandes (Google)" <joel@...lfernandes.org>
To:     linux-kernel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>
Cc:     rcu@...r.kernel.org
Subject: [PATCH 6/6] rcu: Add comment to rcu_do_batch() identifying rcuoc code path

From: "Paul E. McKenney" <paulmck@...nel.org>

This commit adds a comment to help explain why the "else" clause of the
in_serving_softirq() "if" statement does not need to enforce a time limit.
The reason is that this "else" clause handles rcuoc kthreads that do not
block handlers for other softirq vectors.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 kernel/rcu/tree.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8e880c09ab59..06cc6a6ad819 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2131,6 +2131,8 @@ static void rcu_do_batch(struct rcu_data *rdp)
 				break;
 			}
 		} else {
+			// In rcuoc context, so no worries about depriving
+			// other softirq vectors of CPU cycles.
 			local_bh_enable();
 			lockdep_assert_irqs_enabled();
 			cond_resched_tasks_rcu_qs();
-- 
2.40.0.rc1.284.g88254d51c5-goog