linux-kernel - [PATCH rcu 10/10] rcu: Use _full() API to debug synchronize

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Message-ID: <20250305030505.94059-11-boqun.feng@gmail.com>
Date: Tue,  4 Mar 2025 19:05:05 -0800
From: Boqun Feng <boqun.feng@...il.com>
To: rcu@...r.kernel.org
Cc: Petr Mladek <pmladek@...e.com>,	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,	Boqun Feng <boqun.feng@...il.com>,
	Uladzislau Rezki <urezki@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,	Davidlohr Bueso <dave@...olabs.net>,
	Shuah Khan <shuah@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Clark Williams <clrkwllms@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,	Yuntao Wang <ytcoode@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Guo Weikang <guoweikang.kernel@...il.com>,	KP Singh <kpsingh@...nel.org>,
	Huang Shijie <shijie@...amperecomputing.com>,
	Raul E Rangel <rrangel@...omium.org>,
	Joel Granados <joel.granados@...nel.org>,
	Anna Schumaker <anna.schumaker@...cle.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Thomas Weißschuh <linux@...ssschuh.net>,
	zhangguopeng <zhangguopeng@...inos.cn>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Neeraj Upadhyay (AMD)" <neeraj.iitr10@...il.com>,
	linux-kernel@...r.kernel.org,	linux-kselftest@...r.kernel.org,
	linux-rt-devel@...ts.linux.dev,	cheung wall <zzqq0103.hey@...il.com>
Subject: [PATCH rcu 10/10] rcu: Use _full() API to debug synchronize_rcu()

From: "Uladzislau Rezki (Sony)" <urezki@...il.com>

Switch for using of get_state_synchronize_rcu_full() and
poll_state_synchronize_rcu_full() pair to debug a normal
synchronize_rcu() call.

Just using "not" full APIs to identify if a grace period is
passed or not might lead to a false-positive kernel splat.

It can happen, because get_state_synchronize_rcu() compresses
both normal and expedited states into one single unsigned long
value, so a poll_state_synchronize_rcu() can miss GP-completion
when synchronize_rcu()/synchronize_rcu_expedited() concurrently
run.

To address this, switch to poll_state_synchronize_rcu_full() and
get_state_synchronize_rcu_full() APIs, which use separate variables
for expedited and normal states.

Reported-by: cheung wall <zzqq0103.hey@...il.com>
Closes: https://lore.kernel.org/lkml/Z5ikQeVmVdsWQrdD@pc636/T/
Fixes: 988f569ae041 ("rcu: Reduce synchronize_rcu() latency")
Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
Reviewed-by: Paul E. McKenney <paulmck@...nel.org>
Link: https://lore.kernel.org/r/20250227131613.52683-3-urezki@gmail.com
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 include/linux/rcupdate_wait.h | 3 +++
 kernel/rcu/tree.c             | 8 +++-----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/linux/rcupdate_wait.h b/include/linux/rcupdate_wait.h
index f9bed3d3f78d..4c92d4291cce 100644
--- a/include/linux/rcupdate_wait.h
+++ b/include/linux/rcupdate_wait.h
@@ -16,6 +16,9 @@
 struct rcu_synchronize {
 	struct rcu_head head;
 	struct completion completion;
+
+	/* This is for debugging. */
+	struct rcu_gp_oldstate oldstate;
 };
 void wakeme_after_rcu(struct rcu_head *head);
 
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 131fb463ba68..fb98d4d9d9c9 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1612,12 +1612,10 @@ static void rcu_sr_normal_complete(struct llist_node *node)
 {
 	struct rcu_synchronize *rs = container_of(
 		(struct rcu_head *) node, struct rcu_synchronize, head);
-	unsigned long oldstate = (unsigned long) rs->head.func;
 
 	WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) &&
-		!poll_state_synchronize_rcu(oldstate),
-		"A full grace period is not passed yet: %lu",
-		rcu_seq_diff(get_state_synchronize_rcu(), oldstate));
+		!poll_state_synchronize_rcu_full(&rs->oldstate),
+		"A full grace period is not passed yet!\n");
 
 	/* Finally. */
 	complete(&rs->completion);
@@ -3218,7 +3216,7 @@ static void synchronize_rcu_normal(void)
 	 * snapshot before adding a request.
 	 */
 	if (IS_ENABLED(CONFIG_PROVE_RCU))
-		rs.head.func = (void *) get_state_synchronize_rcu();
+		get_state_synchronize_rcu_full(&rs.oldstate);
 
 	rcu_sr_normal_add_req(&rs);
 
-- 
2.48.1