linux-kernel - [PATCH rcu 3/7] rcu: Allow short-circuiting of synchronize_rcu_tasks

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Message-Id: <20241009180045.777721-3-paulmck@kernel.org>
Date: Wed,  9 Oct 2024 11:00:41 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: frederic@...nel.org,
	rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	rostedt@...dmis.org,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>
Subject: [PATCH rcu 3/7] rcu: Allow short-circuiting of synchronize_rcu_tasks_rude()

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>
---
 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 6333f4ccf024b..dd9730fd44fbe 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);

-- 
2.40.1