linux-kernel - [PATCH 4/4] rcu: Use _full() API to debug synchronize

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Message-Id: <20250123185828.460836-4-urezki@gmail.com>
Date: Thu, 23 Jan 2025 19:58:28 +0100
From: "Uladzislau Rezki (Sony)" <urezki@...il.com>
To: "Paul E . McKenney" <paulmck@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>
Cc: RCU <rcu@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Cheung Wall <zzqq0103.hey@...il.com>,
	Neeraj upadhyay <Neeraj.Upadhyay@....com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: [PATCH 4/4] rcu: Use _full() API to debug synchronize_rcu()

Switch for using of get_state_synchronize_rcu_full() and
poll_state_synchronize_rcu_full() pair for 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 kernel splat.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
---
 include/linux/rcupdate_wait.h | 4 ++++
 kernel/rcu/tree.c             | 8 +++-----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/linux/rcupdate_wait.h b/include/linux/rcupdate_wait.h
index f9bed3d3f78d..a16fc2a9a7d7 100644
--- a/include/linux/rcupdate_wait.h
+++ b/include/linux/rcupdate_wait.h
@@ -16,6 +16,10 @@
 struct rcu_synchronize {
 	struct rcu_head head;
 	struct completion completion;
+#ifdef CONFIG_PROVE_RCU
+	/* This is for testing. */
+	struct rcu_gp_oldstate oldstate;
+#endif
 };
 void wakeme_after_rcu(struct rcu_head *head);
 
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 2795d6b5109c..0ae90089ef09 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);
@@ -3214,7 +3212,7 @@ 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);
 
-- 
2.39.5