linux-kernel - [PATCH rcu 3/6] rcu-tasks: Remove preemption disablement around srcu_read

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Message-Id: <20230105004501.1771332-5-paulmck@kernel.org>
Date:   Wed,  4 Jan 2023 16:44:53 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...a.com,
        rostedt@...dmis.org, Frederic Weisbecker <frederic@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: [PATCH rcu 3/6] rcu-tasks: Remove preemption disablement around srcu_read_[un]lock() calls

From: Frederic Weisbecker <frederic@...nel.org>

Ever since the following commit:

	5a41344a3d83 ("srcu: Simplify __srcu_read_unlock() via this_cpu_dec()")

SRCU doesn't rely anymore on preemption to be disabled in order to
modify the per-CPU counter. And even then it used to be done from the API
itself.

Therefore and after checking further, it appears to be safe to remove
the preemption disablement around __srcu_read_[un]lock() in
exit_tasks_rcu_start() and exit_tasks_rcu_finish()

Suggested-by: Boqun Feng <boqun.feng@...il.com>
Suggested-by: Paul E. McKenney <paulmck@...nel.org>
Suggested-by: Neeraj Upadhyay <quic_neeraju@...cinc.com>
Cc: Lai Jiangshan <jiangshanlai@...il.com>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tasks.h | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 50d4c0ec7a89f..fbaed2637a7ff 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1008,9 +1008,7 @@ EXPORT_SYMBOL_GPL(show_rcu_tasks_classic_gp_kthread);
  */
 void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
 {
-	preempt_disable();
 	current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
-	preempt_enable();
 }
 
 /*
@@ -1022,9 +1020,7 @@ void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu)
 {
 	struct task_struct *t = current;
 
-	preempt_disable();
 	__srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx);
-	preempt_enable();
 	exit_tasks_rcu_finish_trace(t);
 }
 
-- 
2.31.1.189.g2e36527f23