linux-kernel - [PATCH 5/5] srcu: Early test SRCU polling start

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Date:   Fri,  9 Apr 2021 00:39:02 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Paul E . McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Josh Triplett <josh@...htriplett.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: [PATCH 5/5] srcu: Early test SRCU polling start

Test early calls to start_poll_synchronize_srcu(), mixed within the
early test to call_srcu(), and make sure that
poll_state_synchronize_srcu() correctly see the expired grace periods
after the srcu_barrier() on late initcall. Normally srcu_barrier()
doesn't wait for callback-less grace periods but early calls to
start_poll_synchronize_srcu() involve empty callbacks.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Lai Jiangshan <jiangshanlai@...il.com>
Cc: Neeraj Upadhyay <neeraju@...eaurora.org>
Cc: Josh Triplett <josh@...htriplett.org>
Cc: Joel Fernandes <joel@...lfernandes.org>
Cc: Uladzislau Rezki <urezki@...il.com>
---
 kernel/rcu/update.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index dd94a602a6d2..7ee57d66a327 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -528,6 +528,7 @@ DEFINE_STATIC_SRCU(early_srcu);
 struct early_boot_kfree_rcu {
 	struct rcu_head rh;
 };
+static unsigned long early_cookie[3];
 
 static void early_boot_test_call_rcu(void)
 {
@@ -536,8 +537,14 @@ static void early_boot_test_call_rcu(void)
 	struct early_boot_kfree_rcu *rhp;
 
 	call_rcu(&head, test_callback);
-	if (IS_ENABLED(CONFIG_SRCU))
+	if (IS_ENABLED(CONFIG_SRCU)) {
+		int i;
+		early_cookie[0] = start_poll_synchronize_srcu(&early_srcu);
 		call_srcu(&early_srcu, &shead, test_callback);
+
+		for (i = 1; i < ARRAY_SIZE(early_cookie); i++)
+			early_cookie[i] = start_poll_synchronize_srcu(&early_srcu);
+	}
 	rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
 	if (!WARN_ON_ONCE(!rhp))
 		kfree_rcu(rhp, rh);
@@ -561,8 +568,11 @@ static int rcu_verify_early_boot_tests(void)
 		early_boot_test_counter++;
 		rcu_barrier();
 		if (IS_ENABLED(CONFIG_SRCU)) {
+			int i;
 			early_boot_test_counter++;
 			srcu_barrier(&early_srcu);
+			for (i = 0; i < ARRAY_SIZE(early_cookie); i++)
+				WARN_ON_ONCE(!poll_state_synchronize_srcu(&early_srcu, early_cookie[i]));
 		}
 	}
 	if (rcu_self_test_counter != early_boot_test_counter) {
-- 
2.25.1