linux-kernel - [PATCH 2/8] rcu: Allow short-circuiting of synchronize_rcu_tasks

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Message-ID: <20241106145911.35503-3-frederic@kernel.org>
Date: Wed,  6 Nov 2024 15:59:05 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: "Paul E. McKenney" <paulmck@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Neeraj Upadhyay <neeraj.upadhyay@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	rcu <rcu@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>
Subject: [PATCH 2/8] rcu: Allow short-circuiting of synchronize_rcu_tasks_rude()

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

There are now architectures for which all deep-idle and entry-exit
functions are properly inlined or marked noinstr.  Such architectures do
not need synchronize_rcu_tasks_rude(), or will not once RCU Tasks has
been modified to pay attention to idle tasks.  This commit therefore
allows a CONFIG_ARCH_HAS_NOINSTR_MARKINGS Kconfig option to turn
synchronize_rcu_tasks_rude() into a no-op.

To facilitate testing, kernels built by rcutorture scripting will enable
RCU Tasks Trace even on systems that do not need it.

[ paulmck: Apply Peter Zijlstra feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@...nel.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 kernel/rcu/tasks.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 6333f4ccf024..dd9730fd44fb 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1398,7 +1398,8 @@ static void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func)
  */
 void synchronize_rcu_tasks_rude(void)
 {
-	synchronize_rcu_tasks_generic(&rcu_tasks_rude);
+	if (!IS_ENABLED(CONFIG_ARCH_WANTS_NO_INSTR) || IS_ENABLED(CONFIG_FORCE_TASKS_RUDE_RCU))
+		synchronize_rcu_tasks_generic(&rcu_tasks_rude);
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_rude);
 
-- 
2.46.0