linux-kernel - [PATCH 3/8] rcu: Permit start_poll_synchronize

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Message-ID: <20241106145911.35503-4-frederic@kernel.org>
Date: Wed,  6 Nov 2024 15:59:06 +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>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Frederic Weisbecker <frederic@...nel.org>
Subject: [PATCH 3/8] rcu: Permit start_poll_synchronize_rcu*() with interrupts disabled

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

The header comment for both start_poll_synchronize_rcu() and
start_poll_synchronize_rcu_full() state that interrupts must be enabled
when calling these two functions, and there is a lockdep assertion in
start_poll_synchronize_rcu_common() enforcing this restriction.  However,
there is no need for this restrictions, as can be seen in call_rcu(),
which does wakeups when interrupts are disabled.

This commit therefore removes the lockdep assertion and the comments.

Reported-by: Kent Overstreet <kent.overstreet@...ux.dev>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 kernel/rcu/tree.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 38b121a77366..13829cf38f52 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4194,7 +4194,6 @@ static void start_poll_synchronize_rcu_common(void)
 	struct rcu_data *rdp;
 	struct rcu_node *rnp;
 
-	lockdep_assert_irqs_enabled();
 	local_irq_save(flags);
 	rdp = this_cpu_ptr(&rcu_data);
 	rnp = rdp->mynode;
@@ -4219,9 +4218,6 @@ static void start_poll_synchronize_rcu_common(void)
  * grace period has elapsed in the meantime.  If the needed grace period
  * is not already slated to start, notifies RCU core of the need for that
  * grace period.
- *
- * Interrupts must be enabled for the case where it is necessary to awaken
- * the grace-period kthread.
  */
 unsigned long start_poll_synchronize_rcu(void)
 {
@@ -4242,9 +4238,6 @@ EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
  * grace period (whether normal or expedited) has elapsed in the meantime.
  * If the needed grace period is not already slated to start, notifies
  * RCU core of the need for that grace period.
- *
- * Interrupts must be enabled for the case where it is necessary to awaken
- * the grace-period kthread.
  */
 void start_poll_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
 {
-- 
2.46.0